英语词源字典 - 在线词源网站

defense (n.)[defense 词源字典]: c. 1300, "forbidding, prohibition," also "action of guarding or protecting," from Old French defense, from Latin defensus, past participle of defendere "ward off, protect" (see defend). But it also arrived (without the final -e) from Old French defens, from Latin defensum "thing protected or forbidden," neuter past participle of defendere.

Defens was assimilated into defense, but not before it inspired the alternative spelling defence, via the same tendency that produced hence (hennis), pence (penies), dunce (Duns). First used 1935 as a euphemism for "national military resources." Defense mechanism in psychology is from 1913. [defense etymology, defense origin, 英语词源]
defenseless (adj.): also defenceless, 1520s, from defense + -less. Related: Defenselessly.
defensible (adj.): late 13c., from Old French defensable, from Late Latin defensibilem, from Latin defens-, past participle stem of defendere (see defend).
defensive: c. 1400 (adj. and noun), from French défensif (14c.), from Medieval Latin defensivus, from defens-, past participle stem of Latin defendere (see defend). Of persons, "alert to reject criticism," from 1919. Related: Defensively; defensiveness.
indefensible (adj.): 1520s, from in- (1) "not, opposite of" + defensible. Related: Indefensibly.
inoffensive (adj.): 1590s, from in- (1) "not, opposite of" + offensive. Related: Inoffensively; inoffensiveness.
offense (n.): late 14c., "hurt, harm, injury, pain," from Old French ofense "offense, insult, wrong" (13c.) and directly from Latin offensa "an offense, injury, affront, crime," literally "a striking against," noun use of fem. past participle of offendere (see offend). Meaning "action of attacking" and "feeling of being hurt" are both first recorded c. 1400. Sense of "breach of the law, transgression" is first recorded late 14c. Sporting sense first recorded 1894.
offensive (adj.): "attacking" (1540s), "insulting" (1570s), both from Middle French offensif (16c.) and directly from Medieval Latin offensivus, from Latin offens-, past participle stem of offendere "offend" (see offend). Related: Offensively; offensiveness.
offensive (n.): "condition of attacking, aggressive action," 1720, from offensive (adj.).
self-defense (n.): 1650s, "act of defending oneself," first attested in Hobbes, from self- + defense. In sports sense, first with reference to fencing (1728), then boxing (1820s).