1640s, "act of struggling against," from obsolete verb reluct "to struggle or rebel against" (1520s), from Latin reluctari "to struggle against, resist, make opposition," from re- "against" (see re-) + luctari "to struggle, wrestle," perhaps shares a common origin with Greek lygos "pliant twig," lygizein "to bend, twist," Old English locc "twist of hair" (see lock, n.2). Meaning "unwillingness" is first attested 1660s. Related: Reluctancy (1620s.).