WordNet (r) 3.0 (2006):

costs
    n 1: pecuniary reimbursement to the winning party for the
         expenses of litigation

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

COSTS, practice. The expenses of a suit or action which may be recovered by
law from the losing party.
     2. At common law, neither the plaintiff nor the defendant could recover
costs eonomine; but in all actions in which damages were recoverable, the
plaintiff, in effect, recovered his costs when he obtained a verdict, for
the jury always computed them in the damages. When the defendant obtained a
verdict, or the plaintiff became non-suit, the former was wholly without
remedy for any expenses he had incurred. It is true, the plaintiff was
amerced pro falso clamore suo, but the amercement was given to the king.
Hull on Costs, 2 2 Arch. Pr. 281.
     3. This defect was afterwards corrected by the statute of Gloucester, 6
Ed. I, c. 1, by which it is enacted that "the demandant in assise of novel
disseisin, in writs of mort d'ancestor, cosinage, aiel and be sail, shall
have damages. And the demandant shall have the costs of the writ purchased,
together with damages, and this act shall hold place in all cases where the
party recovers damages, and every person shall render damages where land is
recovered against him upon his own intrusion, or his own act." About forty-
six years after the passing of this statute, costs were for the first time
allowed in France, by an ordinance of Charles le Bel, (January, 1324.) See
Hardw. Cas. 356; 2 Inst. 283, 288 2 Loisel, Coutumes, 328-9.
     4. The statute of Gloucester has been adopted, substantially, in all
the United States. Though it speaks of the costs of the writ only, it has,
by construction, been extended to the costs of the suit generally. The costs
which are recovered under it are such as shall be allowed by the master or
prothonotary upon taxation, and not those expenses which the. plaintiff may
have. incurred for himself, or the extraordinary fees he may have paid
counsel, or for the loss of his time. 2 Sell. Pr. 429.
     5. Costs are single, when the party receives the same amount he has
expended, to be ascertained by taxation; double, vide Double costs. and
treble, vide Treble costs. Vide, generally, Bouv. Inst. Index, h.t.;
Hullock on Costs; Sayer's Law of Costs; Tidd's Pr. c. 40; 2 Sell. Pr. c. 19;
Archb. Pr. Index, h.t.; Bac. Ab. h.t.; Com. Dig. h.t.; 6 Vin. Ab. 321;
Grah. Pr. c. 23 Chit. Pr. h.t. 1 Salk. 207 1 Supp. to Ves. jr. 109; Amer.
Dig. h.t.; Dane's Ab. h.t.; Harr. Dig. h.t. As to the liability of
executors and administrators for costs, see 1, Chit. R. 628, note; 18 E. C.
L. R. 185; 2 Bay's R. 166, 399; 1 Wash. R. 138; 2 Hen. & Munf. 361, 369; 4
John. R. 190; 8 John. R. 389; 2 John. Ca. 209. As to costs in actions qui
tam, see Esp. on Pen. Act. 154 to 165.