faculty (n.) Look up faculty at Dictionary.com
late 14c., "ability, opportunity, means, resources," from Old French faculte "skill, accomplishment, learning" (14c., Modern French faculté) and directly from Latin facultatem (nominative facultas) "power, ability, capability, opportunity; sufficient number, abundance, wealth," from *facli-tat-s, from facilis "easy to do," of persons, "pliant, courteous, yielding," from facere "to do" (from PIE root *dhe- "to set, put").

Academic sense "branch of knowledge" (late 14c.) was in Old French and probably was the earliest in English (it is attested in Anglo-Latin from late 12c.), on notion of "ability in knowledge" or "body of persons on whom are conferred specific professional powers." Originally each department was a faculty; the use in reference to the whole teaching staff of an entire college dates from 1767. Related: Facultative. The Latin words facultas and facilitas "were originally different forms of the same word; the latter, owing to its more obvious relationship to the adj., retained the primary sense of 'easiness', which the former had ceased to have before the classical period." [OED]