faculty (n.)
late 14c., "ability, means, resources," from Old French faculté (14c.) "skill, accomplishment, learning," and directly from Latin facultatem (nominative facultas) "power, ability, wealth," from *facli-tat-s, from facilis (see facile).

Academic sense "branch of knowledge" probably was the earliest in English (attested in Anglo-Latin from late 12c.), on notion of "ability in knowledge." Originally each department was a faculty; the use in reference to the whole teaching staff of a college dates from 1767.