attendee n.

c. 1300, "be subject to" (obsolete); early 14c., "direct one's mind or energies" (archaic), from Old French atendre "to expect, wait for, pay attention" (12c., Modern French attendre) and directly from Latin attendere "give heed to," literally "to stretch toward," from ad "to, toward" (see ad-) + tendere "stretch" (from PIE root *ten- "to stretch"). The notion is of "stretching" one's mind toward something.

The sense of "take care of, wait upon" is from mid-14c.; that of "endeavor to do" is from c. 1400. The meaning "to pay attention" is from early 15c.; that of "accompany and render service to" (someone) is from mid-15c., as is that of "be in attendance." The meaning "to accompany or follow as a consequent" is from 1610s. Related: Attended; attending.

word-forming element in legal English (and in imitation of it), representing the Anglo-French -é ending of past participles used as nouns (compare -y (3)). As these sometimes were coupled with agent nouns in -or, the two suffixes came to be used as a pair to denote the initiator and the recipient of an action.

Not to be confused with the French -ée that is a feminine noun ending (as in fiancée), which is from Latin -ata.