late 14c., "to put (something) into the body or substance of (something else), blend; absorb, eat," also "solidify, harden," often in medical writing, from Late Latin incorporatus, past participle of incorporare "unite into one body, embody, include," from Latin in- "into, in, on, upon" (from PIE root *en "in") + verb from corpus (genitive corporis) "body" (from PIE root *kwrep- "body, form, appearance").
Meaning "to legally form a body politic with perpetual succession and power to act as one person, establish as a legal corporation" is from mid-15c. (A verb corporate was used in this sense from early 15c.) Intransitive sense of "unite with another body so as to become part of it" is from 1590s. Related: Incorporated; incorporating.