Clientele
mid 16th century (in the sense ‘clientship, patronage’): via French from Latin clientela ‘clientship’, from cliens, client- (see client).
wiktionary
Borrowed from French clientèle, ultimately from Latin cliēns (English client).
etymonline
clientele (n.)
1560s, "body of professed adherents, clients collectively under the patronage of someone," from French clientèle (16c.), from Latin clientela "relationship between dependent and patron; body of clients," from clientem (nominative cliens, "follower, retainer;" see client).
The word is said in OED to apparently have become obsolete after 17c., and the main modern meaning "customers, those who regularly patronize a business or professional" is from 1857, perhaps a reborrowing from French (it was used in English in italics as a foreign word from 1836).
Clientage is attested from 1630s as "a body of clients;" clientship from 1640s as "condition of being a client."
