inveterate (in-VET-ehr-it) adjective
Firmly established; habitual.
[From Middle English, from Latin inveteratus, past participle of inveterare (to grow old), in-, + vetus, stem of veter- (old). Ultimately from Indo-European root wet- (year) that is also the source of such words as veteran, veal (in the sense of yearling), and veterinary (relating to the beasts of burden, perhaps alluding to old cattle).]
"Men met each other with erected look,
The steps were higher that they took;
Friends to congratulate their friends made haste,
And long inveterate foes saluted as they pass'd."
-- John Dryden; Threnodia Augustalis; 1685.