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.
<a href="https://www.etymonline.com/word/mortgagee">Etymology of mortgagee by etymonline</a>
Harper, D. (n.d.). Etymology of mortgagee. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/mortgagee