The Collaborative International Dictionary of English v.0.48:

Purchaser \Pur"chas*er\, n.
   1. One who purchases; one who acquires property for a
      consideration, generally of money; a buyer; a vendee.
      [1913 Webster]

   2. (Law) One who acquires an estate in lands by his own act
      or agreement, or who takes or obtains an estate by any
      means other than by descent or inheritance.
      [1913 Webster]

WordNet (r) 3.0 (2006):

purchaser
    n 1: a person who buys [syn: buyer, purchaser, emptor,
         vendee]

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

PURCHASER, contracts. A buyer, a vendee.
     2. It is a general rule that all persons, capable of entering into
contracts, may become purchasers both of real and personal property.
     3. But to this rule there are several exceptions. 1. There is a class
of persons who are incapable of purchasing except sub modo; and, 2. Another
class, who, in consequence of their peculiar relation with regard to the
owners of the thing sold, are totally incapable of becoming purchasers,
while that relation exists.
     4.-1. To the first class belong, 1st. Infants under the age of twenty-
one years, who may purchase, and at their full age bind themselves by
agreeing to the bargain, or waive the purchase without alleging any cause
for so doing. If they do not agree to the purchase after their full age,
their heirs may waive it in the same manner as they themselves could have
done. Cro. Jac. 320; Rolle's Ab. 731 K; Co. Litt. 2 b; 6 Mass. R. 80; 6
John. R. 257.
     5.-2d. Femes covert, who are capable of purchasing but their husbands
may disagree to the contract, and divest the whole estate; the husband may
further recover back the purchase-money. 1 Ld. Raym. 224; 1 Madd. Ch. R.
258; 6 Binn. R. 429. When the husband neither, agrees nor disagrees, the
purchase will be valid. After the husband's death, the wife may waive the
purchase without assigning any cause for it, although the husband may have
agreed to it; and if, after her husband's death, she do not agree to it, her
heirs may waive it. Co. Lift. 3 a; Dougl. R. 452.
     6.-3d. Lunatics, or idiots, who are capable of purchasing. It seems
that although they recover their senses, they cannot of themselves waive the
purchase; yet if, after recovering their senses, they agree to it, their
heirs cannot set it aside. 2 Bl. Com. 291; and see 3 Day's R. 101. Their
heirs may avoid the purchase when they die during their lunacy or idiocy.
Co. Litt. 2 b.
     7.-2. It is a general rule that trustees 2 Bro. C. C. 400; 3 Bro. C. C.
483; 1 John. Ch. R. 36; 3 Desaus. Ch. R. 26; 3 Binn. Y. 59; unless they are
nominally so, to preserve contingent remainders; 11 Ves, Jr. 226; agents; 8
Bro. P. C; 42; 13 Ves. Jr. 95; Story, Ag. Sec. 9; commissioners of
bankrupts; assignees of bankrupts; solicitors to the commission; 6 Ves. Jr.
630, n. b.; auctioneers and creditors who have been consulted as to the mode
of sale; 6 Ves. Jr. 617; 2 Johns. Ch. R. 257; or any other persons who, by
their connexion with the owner, or by being employed concerning his affairs,
have acquired a knowledge of his property, are generally incapable of
purchasing such property themselves. And so stern is the rule, that when a
person cannot purchase the estate himself, he cannot buy it, as agent for
another; 9 Ves. Jr. 248; nor perhaps employ a third person to bid for it on
behalf of a stranger; 10 Ves. Jr. 381 for no court is equal to the
examination and ascertainment of the truth in a majority of such cases. 8
Ves. Jr. 345.
     8. The obligations of the purchaser resulting from the contract of
sale, are, 1. To pay the price agreed upon in the contract. 2. To take away
the thing purchased, unless otherwise agreed upon; and, 3. To indemnify the
seller for any expenses he may have incurred to preserve it for him. Vide
Sugd. on Vend. Index, h.t.; Ross on Vend. Index, h.t.; Long on Sales, Index,
h.t.;  2 Supp. to Ves. Jr. 449, 267, 478; Yelv. 45; 2 Ves. Jr. 100; 8 Coin.
Dig. 349; 3 Com. Dig. 108.