Origin of accustomed
late 15c., "made customary, habitual," past participle adjective from accustom (v.).
Used to something or someone; having the habit of doing something. For example, In Spain we gave up our usual schedule and became accustomed to eating dinner at 10 p.m. Professor Higgins in the musical My Fair Lady (1956) ruefully sang the song “I've Grown Accustomed to Her Face” after his protégé Eliza walked out on him. [Second half of 1400s]