The Collaborative International Dictionary of English v.0.48:

Business \Busi"ness\ (b[i^]z"n[e^]s), n.; pl. Businesses
   (b[i^]z"n[e^]s*[e^]z). [From Busy.]
   1. That which busies one, or that which engages the time,
      attention, or labor of any one, as his principal concern
      or interest, whether for a longer or shorter time;
      constant employment; regular occupation; as, the business
      of life; business before pleasure.
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            Wist ye not that I must be about my Father's
            business?                             --Luke ii. 49.
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   2. Any particular occupation or employment engaged in for
      livelihood or gain, as agriculture, trade, art, or a
      profession. "The business of instruction." --Prescott.
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   3. Financial dealings; buying and selling; traffic in
      general; mercantile transactions.
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            It seldom happens that men of a studious turn
            acquire any degree of reputation for their knowledge
            of business.                          --Bp. Popteus.
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   4. That which one has to do or should do; special service,
      duty, or mission.
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            The daughter of the King of France,
            On serious business, craving quick despatch,
            Importunes personal conference.       --Shak.
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            What business has the tortoise among the clouds?
                                                  --L'Estrange.
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   5. Affair; concern; matter; -- used in an indefinite sense,
      and modified by the connected words.
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            It was a gentle business, and becoming
            The action of good women.             --Shak.
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            Bestow
            Your needful counsel to our business. --Shak.
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   6. (Drama) The position, distribution, and order of persons
      and properties on the stage of a theater, as determined by
      the stage manager in rehearsal.
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   7. Care; anxiety; diligence. [Obs.] --Chaucer.
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   To do one's business, to ruin one. [Colloq.] --Wycherley.

   To make (a thing) one's business, to occupy one's self with
      a thing as a special charge or duty. [Colloq.]

   To mean business, to be earnest. [Colloq.]
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   Syn: Affairs; concern; transaction; matter; engagement;
        employment; calling; occupation; trade; profession;
        vocation; office; duty.
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WordNet (r) 3.0 (2006):

business
    n 1: a commercial or industrial enterprise and the people who
         constitute it; "he bought his brother's business"; "a small
         mom-and-pop business"; "a racially integrated business
         concern" [syn: business, concern, business concern,
         business organization, business organisation]
    2: the activity of providing goods and services involving
       financial and commercial and industrial aspects; "computers
       are now widely used in business" [syn: commercial
       enterprise, business enterprise, business]
    3: the principal activity in your life that you do to earn
       money; "he's not in my line of business" [syn: occupation,
       business, job, line of work, line]
    4: a rightful concern or responsibility; "it's none of your
       business"; "mind your own business"
    5: an immediate objective; "gossip was the main business of the
       evening"
    6: the volume of commercial activity; "business is good today";
       "show me where the business was today"
    7: business concerns collectively; "Government and business
       could not agree" [syn: business, business sector]
    8: customers collectively; "they have an upper class clientele"
       [syn: clientele, patronage, business]
    9: incidental activity performed by an actor for dramatic
       effect; "his business with the cane was hilarious" [syn:
       business, stage business, byplay]