inveterate (adj.)
late 14c., "old," from Latin inveteratus "of long standing, chronic, old," past participle of inveterare "become old in," from in- "in, into" (from PIE root *en "in") + verb from vetus (genitive veteris) "old" (see veteran). From early 15c. as "firmly established by long continuance;" from c. 1500, of persons, "hardened, confirmed" (in habit, etc.). Related: Inveterateness.