From The Collaborative International Dictionary of English v.0.48:

Employment \Em*ploy"ment\, n.
   1. The act of employing or using; also, the state of being
      employed.
      [1913 Webster]

   2. That which engages or occupies; that which consumes time
      or attention; office or post of business; service; as,
      agricultural employments; mechanical employments; public
      employments; in the employment of government.
      [1913 Webster]

            Cares are employments, and without employ
            The soul is on a rack.                --Young.

   Syn: Work; business; occupation; vocation; calling; office;
        service; commission; trade; profession.
        [1913 Webster]

From WordNet (r) 2.0:

employment
     n 1: the state of being employed or having a job; "they are
          looking for employment"; "he was in the employ of the
          city" [syn: employ] [ant: unemployment]
     2: the occupation for which you are paid; "he is looking for
        employment"; "a lot of people are out of work" [syn: work]
     3: the act of giving someone a job [syn: engagement]
     4: the act of using; "he warned against the use of narcotic
        drugs"; "skilled in the utilization of computers" [syn: use,
         usage, utilization, utilisation, exercise]

From Moby Thesaurus II by Grady Ward, 1.0:

142 Moby Thesaurus words for "employment":
   act, acting, action, active use, activism, activities, activity,
   affair, affairs, appliance, application, appointment, assignment,
   attendance, bag, behavior, berth, bespeaking, billet, booking,
   briefing, business, calling, commerce, concern, concernment,
   consumption, craft, dirty work, disposition, doing, donkeywork,
   drudgery, employ, engagement, engaging, enlistment, enrollment,
   enterprise, exercise, exercising, exertion, exploitation, fag,
   fatigue, function, functioning, gig, good use, grind, handiwork,
   handling, handwork, hard usage, hard use, hire, hiring, ill use,
   implementation, incumbency, industry, interest, job, labor, lick,
   lick of work, line, livelihood, lookout, management, manipulation,
   manual labor, matter, metier, ministration, ministry, mission,
   misuse, moil, moonlighting, movements, occupation, office, opening,
   operation, operations, peonage, place, play, position, post,
   practice, praxis, preengagement, profession, purpose, pursuit,
   racket, rat race, recruitment, reservation, retaining, retainment,
   rough usage, scut work, second job, serfdom, service, servitium,
   servitorship, servitude, situation, skill, slavery, spadework,
   station, stroke, stroke of work, sweat, swing, taking on, task,
   tendance, tenure, thing, tiresome work, toil, trade, travail,
   treadmill, undertaking, usage, use, using, using up, utilization,
   vacancy, vocation, work, working, workings, wrong use

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

EMPLOYMENT. An employment is an office; as, the secretary of the treasury 
has a laborious and responsible employment; an agency, as, the employment of 
an auctioneer; it signifies also the act by which one is engaged to do 
something. 2 Mart. N. S. 672; 2 Harr. Cond. Lo. R. 778. 
     2. The employment of a printer to publish the laws of the United 
States, is not an office. 17 S. & R. 219, 223. See Appointment.