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."