What does Boxing Day have to do with boxing?
late 14c., "grasped by the understanding" (rather than by the senses), from Old French intellectuel and directly from Latin intellectualis "relating to the understanding," from intellectus "discernment, understanding," from past participle stem of intelligere "to understand, discern" (see intelligence). Intellectual property attested from 1845. Other adjective formations included intellective (late 15c.), intellectile (1670s).
1590s, "mind, intellect," from intellectual (adj.); sense of "an intellectual person" is from 1650s. Related: Intellectuals.
A person who engages in academic study or critical evaluation of ideas and issues. (See intelligentsia.)