The Collaborative International Dictionary of English v.0.48:

Buy \Buy\, v. i.
   To negotiate or treat about a purchase.
   [1913 Webster]

         I will buy with you, sell with you.      --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Buy \Buy\ (b[imac]), v. t. [imp. & p. p. Bought (b[add]t); p.
   pr. & vb. n. Buying (b[imac]"[i^]ng).] [OE. buggen, buggen,
   bien, AS. bycgan, akin to OS. buggean, Goth. bugjan.]
   1. To acquire the ownership of (property) by giving an
      accepted price or consideration therefor, or by agreeing
      to do so; to acquire by the payment of a price or value;
      to purchase; -- opposed to sell.
      [1913 Webster]

            Buy what thou hast no need of, and ere long thou
            wilt sell thy necessaries.            --B. Franklin.
      [1913 Webster]

   2. To acquire or procure by something given or done in
      exchange, literally or figuratively; to get, at a cost or
      sacrifice; to buy pleasure with pain.
      [1913 Webster]

            Buy the truth and sell it not; also wisdom, and
            instruction, and understanding.       --Prov. xxiii.
                                                  23.
      [1913 Webster]

   To buy again. See Againbuy. [Obs.] --Chaucer.

   To buy off.
      (a) To influence to compliance; to cause to bend or yield
          by some consideration; as, to buy off conscience.
      (b) To detach by a consideration given; as, to buy off one
          from a party.

   To buy out
      (a) To buy off, or detach from. --Shak.
      (b) To purchase the share or shares of in a stock, fund,
          or partnership, by which the seller is separated from
          the company, and the purchaser takes his place; as, A
          buys out B.
      (c) To purchase the entire stock in trade and the good
          will of a business.

   To buy in, to purchase stock in any fund or partnership.

   To buy on credit, to purchase, on a promise, in fact or in
      law, to make payment at a future day.

   To buy the refusal (of anything), to give a consideration
      for the right of purchasing, at a fixed price, at a future
      time.
      [1913 Webster]

WordNet (r) 3.0 (2006):

buy
    n 1: an advantageous purchase; "she got a bargain at the
         auction"; "the stock was a real buy at that price" [syn:
         bargain, buy, steal]
    v 1: obtain by purchase; acquire by means of a financial
         transaction; "The family purchased a new car"; "The
         conglomerate acquired a new company"; "She buys for the big
         department store" [syn: buy, purchase] [ant: sell]
    2: make illegal payments to in exchange for favors or influence;
       "This judge can be bought" [syn: bribe, corrupt, buy,
       grease one's palms]
    3: be worth or be capable of buying; "This sum will buy you a
       ride on the train"
    4: acquire by trade or sacrifice or exchange; "She wanted to buy
       his love with her dedication to him and his work"
    5: accept as true; "I can't buy this story"

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "buy":
   abide by, accede, accept, accept for gospel, accept implicitly,
   acclaim, acquiesce, acquiesce in, acquire, advantageous purchase,
   agree, agree to, agree with, applaud, approach, assent, bargain,
   be certain, believe, believe without reservation, bribe, buy back,
   buy in, buy into, buy off, buy on credit, buy up, buying,
   buying power, buying up, catalog buying, cheer, coemption,
   complete a purchase, comply, consent, consumer power,
   consumer sovereignty, consumerism, corner, cornering, corrupt,
   credit, emption, engross, fix, get, get at, get to, give faith to,
   give the nod, good buy, good pennyworth, grease, grease the palm,
   hail, have, hire purchase, hold with, impulse buying, in toto,
   installment buying, lubricate, mail-order buying, make a buy,
   marketing, money illusion, monopolize, nod, nod assent, obtain,
   pay off, pennyworth, procure, purchase, purchasing,
   purchasing power, put faith in, reach, rebuy, rebuying, receive,
   redeem, regrate, repurchase, set store by, shopping,
   shopping spree, sop, square, steal, suborn, subscribe to, swallow,
   take, take care of, take for granted, take kindly to,
   take on faith, take on trust, take stock in, tamper with,
   tickle the palm, trust, vote for, welcome, window-shopping, yes,
   yield assent