in·vet·er·ate / inˈvetərit/ • adj. having a particular habit, activity, or interest that is long-established and unlikely to change: he was an inveterate gambler. ∎  (of a feeling or habit) long-established and unlikely to change.DERIVATIVES: in·vet·er·a·cy / -rəsē/ n.in·vet·er·ate·ly adv.

inveterate established by age or long standing; obstinately embittered. XVI. — L. inveterātus, ppl. adj. of inveterāre make old, f. IN-1 + vetus, veter- old; see -ATE2.
Hence inveteracy XVII.