The Collaborative International Dictionary of English v.0.48:

Lesion \Le"sion\ (l[=e]"zh[u^]n), n. [F. l['e]sion, L. laesio,
   fr. laedere, laesum, to hurt, injure.]
   A hurt; an injury. Specifically:
   (a) (Civil Law) Loss sustained from failure to fulfill a
       bargain or contract. --Burrill.
   (b) (Med.) Any morbid change in the exercise of functions or
       the texture of organs. --Dunglison.
       [1913 Webster]

WordNet (r) 3.0 (2006):

lesion
    n 1: any localized abnormal structural change in a bodily part
    2: an injury to living tissue (especially an injury involving a
       cut or break in the skin) [syn: wound, lesion]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "lesion":
   abrasion, abscess, ache, aching, aposteme, bed sore, blain, bleb,
   blemish, blister, blow, boil, break, bubo, bulla, bunion, burn,
   canker, canker sore, carbuncle, chafe, chancre, chancroid, check,
   chilblain, chip, cold sore, concussion, crack, crackle, cramp,
   craze, cut, distress, dolor, eschar, felon, fester, festering,
   fever blister, fistula, flash burn, fracture, fray, frazzle,
   furuncle, furunculus, gall, gash, gathering, grief, gumboil,
   hemorrhoids, hurt, incision, injury, kibe, laceration,
   mortal wound, mutilation, nasty blow, pain, pang, papula, papule,
   paronychia, parulis, passion, petechia, piles, pimple, pock, polyp,
   puncture, pustule, rent, rip, rising, run, rupture, scab, scald,
   scorch, scrape, scratch, scuff, second-degree burn, shock, slash,
   soft chancre, sore, sore spot, spasm, stab, stab wound, stigma,
   stress, stress of life, stroke, sty, suffering, suppuration,
   swelling, tear, tender spot, third-degree burn, throes, trauma,
   tubercle, ulcer, ulceration, wale, welt, wheal, whelk, whitlow,
   wound, wounds immedicable, wrench



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

LESION, contracts. In the civil law this term is used to signify the injury
suffered, in consequence of inequality of situation, by one who does not
receive a full equivalent for what he gives in a commutative contract.
     2. The remedy given for this injury, is founded on its being the effect
of implied error or imposition; for in every commutative contract,
equivalents are supposed to be given and received. Louis. Code, 1854.
Persons of full age, however, are not allowed in point of law to object to
their agreements as being injurious, unless the injury be excessive. Poth.
Oblig. P. 1, c. 1, s. 1, art. 3, Sec. 4. But minors are admitted to
restitution, not only against any excessive inequality, but against any
inequality whatever. Poth. Oblig. P. 1, c. 1, s. 1, art. 3, Sec. 5; Louis.
Code, art. 1858.
     3. Courts of chancery relieve upon terms of redemption and set aside
contracts entered into by expectant heirs dealing for their expectancies, on
the ground of mere inadequacy of price. 1 Vern. 167; 2 Cox, 80; 2 Cas. in
Ch. 136; 1 Vern. 141; 2 Vern. 121; 2 Freem. 111; 2 Vent. 359; 2 Vern. 14; 2
Rep. in Ch. 396; 1 P. W. 312; 1 Bro. C. C. 7; 3 P. Wms. 393, n.; 2 Atk. 133;
2 Ves. 125; 1 Atk. 301; 1 Wils. 286; 1 Wils. 320; 1 Bro. P. 6. ed. Toml.
198; 1 Bro. C. C. 1; 16 Ves. 512; Sugd. on Vend. 231, n. k.; 1 Ball & B.
330; Wightw. 25; 3 Ves. & Bea. 117; 2 Swanst. R. 147, n.; Fonb. notes to the
Treatise of Equity, B, 1, c. 2, s. 9. A contract cannot stand where the
party has availed himself of a confidential situation, in order to obtain
some selfish advantage. Note to Crowe v. Ballard. 1 Ves. jun. 125; 1 Hov.
Supp. 66, 7. Note to Wharton v. May. 5 Ves. 27; 1 Hov. Supp. 378. See
Catching bargain; Fraud; Sale.