From The Collaborative International Dictionary of English v.0.48:

Single \Sin"gle\, a. [L. singulus, a dim. from the root in
   simplex simple; cf. OE. & OF. sengle, fr. L. singulus. See
   Simple, and cf. Singular.]
   1. One only, as distinguished from more than one; consisting
      of one alone; individual; separate; as, a single star.
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            No single man is born with a right of controlling
            the opinions of all the rest.         --Pope.
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   2. Alone; having no companion.
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            Who single hast maintained,
            Against revolted multitudes, the cause
            Of truth.                             --Milton.
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   3. Hence, unmarried; as, a single man or woman.
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            Grows, lives, and dies in single blessedness.
                                                  --Shak.
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            Single chose to live, and shunned to wed. --Dryden.
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   4. Not doubled, twisted together, or combined with others;
      as, a single thread; a single strand of a rope.
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   5. Performed by one person, or one on each side; as, a single
      combat.
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            These shifts refuted, answer thy appellant, . . .
            Who now defles thee thrice ti single fight.
                                                  --Milton.
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   6. Uncompounded; pure; unmixed.
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            Simple ideas are opposed to complex, and single to
            compound.                             --I. Watts.
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   7. Not deceitful or artful; honest; sincere.
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            I speak it with a single heart.       --Shak.
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   8. Simple; not wise; weak; silly. [Obs.]
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            He utters such single matter in so infantly a voice.
                                                  --Beau. & Fl.
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   Single ale, Single beer, or Single drink, small ale,
      etc., as contrasted with double ale, etc., which is
      stronger. [Obs.] --Nares.

   Single bill (Law), a written engagement, generally under
      seal, for the payment of money, without a penalty.
      --Burril.

   Single court (Lawn Tennis), a court laid out for only two
      players.

   Single-cut file. See the Note under 4th File.

   Single entry. See under Bookkeeping.

   Single file. See under 1st File.

   Single flower (Bot.), a flower with but one set of petals,
      as a wild rose.

   Single knot. See Illust. under Knot.

   Single whip (Naut.), a single rope running through a fixed
      block.
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From The Collaborative International Dictionary of English v.0.48:

Single \Sin"gle\, v. i.
   To take the irrregular gait called single-foot; -- said of a
   horse. See Single-foot.
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         Many very fleet horses, when overdriven, adopt a
         disagreeable gait, which seems to be a cross between a
         pace and a trot, in which the two legs of one side are
         raised almost but not quite, simultaneously. Such
         horses are said to single, or to be single-footed. --W.
                                                  S. Clark.
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From The Collaborative International Dictionary of English v.0.48:

Single \Sin"gle\, n.
   1. A unit; one; as, to score a single.
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   2. pl. The reeled filaments of silk, twisted without doubling
      to give them firmness.
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   3. A handful of gleaned grain. [Prov. Eng. & Scot.]
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   4. (Law Tennis) A game with but one player on each side; --
      usually in the plural.
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   5. (Baseball) A hit by a batter which enables him to reach
      first base only.
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From The Collaborative International Dictionary of English v.0.48:

Single \Sin"gle\, v. t. [imp. & p. p. Singled; p. pr. & vb. n.
   Singling.]
   1. To select, as an individual person or thing, from among a
      number; to choose out from others; to separate.
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            Dogs who hereby can single out their master in the
            dark.                                 --Bacon.
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            His blood! she faintly screamed her mind
            Still singling one from all mankind.  --More.
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   2. To sequester; to withdraw; to retire. [Obs.]
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            An agent singling itself from consorts. --Hooker.
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   3. To take alone, or one by one.
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            Men . . . commendable when they are singled.
                                                  --Hooker.
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From WordNet (r) 2.0:

single
     adj 1: existing alone or consisting of one entity or part or aspect
            or individual; "upon the hill stood a single tower";
            "had but a single thought which was to escape"; "a
            single survivor"; "a single serving"; "a single lens";
            "a single thickness" [syn: single(a)] [ant: multiple]
     2: used of flowers having usually only one row or whorl of
        petals; "single chrysanthemums resemble daisies and may
        have more than one row of petals" [ant: double]
     3: not married or related to the unmarried state; "unmarried
        men and women"; "unmarried life"; "sex and the single
        girl"; "single parenthood"; "are you married or single?"
        [syn: unmarried] [ant: married]
     4: characteristic of or meant for a single person or thing; "an
        individual serving"; "separate rooms"; "single occupancy";
        "a single bed" [syn: individual, separate, single(a)]
     5: having uniform application; "a single legal code for all"
        [syn: single(a)]
     6: not divided among or brought to bear on more than one object
        or objective; "judging a contest with a single eye"; "a
        single devotion to duty"; "undivided affection"; "gained
        their exclusive attention" [syn: single(a), undivided,
         exclusive]
     7: involved two individuals; "single combat" [syn: single(a)]
     8: individual and distinct; "pegged down each separate branch
        to the earth"; "a gift for every single child" [syn: separate,
         single(a)]
     n 1: a base hit on which the batter stops safely at first base
     2: the smallest whole number or a numeral representing this
        number; "he has the one but will need a two and three to
        go with it"; "they had lunch at one" [syn: one, 1, I,
         ace, unity]
     v : hit a one-base hit

From Moby Thesaurus II by Grady Ward, 1.0:

122 Moby Thesaurus words for "single":
   a certain, an, any, any one, appropriate, article, atomic, austere,
   bachelorlike, bare, basic, candid, celibataire, celibate,
   characteristic, chaste, choose, cull, distinct, distinctive,
   distinguish, distinguished, either, elementary, entity, especial,
   essential, exclusive, fasten on, fix on, footloose and fancy-free,
   free, fundamental, homely, homespun, homogeneous, husbandless,
   idiocratic, idiosyncratic, in character, individual, indivisible,
   integer, integral, intrinsic, irreducible, isolated, item, lone,
   maiden, maidenly, marked, mere, misogamist, misogynist, module,
   monadic, monastic, monistic, monk, monolithic, nun, of a piece,
   old-maidish, one, only, open, particular, peculiar, person,
   persona, pick, plain, point, priest, primal, primary, proper, pure,
   pure and simple, quintessential, segregate, select, separate,
   severe, simon-pure, simple, single out, singleton, singular, sole,
   solid, solitary, soul, spare, special, specific, spinsterish,
   spinsterlike, spinsterly, spouseless, stark, true to form,
   unadorned, unanalyzable, unattached, uncluttered, undifferenced,
   undifferentiated, undivided, unfettered, uniform, unique, unit,
   unitary, unmarried, unshared, unwed, unwedded, virgin, virginal,
   whole

From Bouvier's Law Dictionary, Revised 6th Ed (1856):

SINGLE. By itself, unconnected. 
     2. A single bill is one without any condition, and does not depend upon 
any future event to give it validity. Single is also applied to an unmarried 
person; as, A B, single woman. Vide Simplex.