late 14c., "cast out," from Latin expellere "drive out, drive away," from ex "out" (see ex-) + pellere "to drive" (from PIE root *pel- (5) "to thrust, strike, drive"). Specific meaning "to eject from a school" is first recorded 1640s. Related: Expelled; expelling.
-ee
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.