word-forming element used in forming nouns from Latin words ending in -atus, -atum (such as estate, primate, senate). Those that came to English via French often arrived with -at, but an -e was added after c. 1400 to indicate the long vowel. The suffix also can mark adjectives formed from Latin past participles in -atus, -ata (such as desolate, moderate, separate); again, they often were adopted in Middle English as -at, with an -e appended after c. 1400.
<a href="https://www.etymonline.com/word/electorate">Etymology of electorate by etymonline</a>
Harper, D. (n.d.). Etymology of electorate. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/electorate