late 14c., "grasped by the understanding" (rather than by the senses), from Old French intellectuel (13c.) and directly from Latin intellectualis "relating to the understanding," from intellectus "discernment, understanding," noun use of past participle of intelligere "to understand, discern" (see intelligence).
Sense of "characterized by a high degree of intellect" is from 1819. Meaning "appealing to or engaging the mental powers" is from 1834. Intellectual property "products of the intellect" is attested from 1845. Adjective formations in the sense "of or pertaining to the intellect" included intellective (early 15c.), intellectile (1670s).
1590s, "mind, intellect, intellectual powers," from intellectual (adj.). The meaning "an intellectual person" is attested from 1650s but was hardly used in that sense in 19c. and the modern use in this sense seems to be a re-coinage from c. 1906. Related: Intellectuals.