The Collaborative International Dictionary of English v.0.48:

Clientele \Cli`en*tele"\ (? or ?), n. [L. clientela: cf. F.
   client[`e]le.]
   1. The condition or position of a client; clientship. [Obs.]
      --Bp. Hall.
      [1913 Webster]

   2. The clients or dependents of a nobleman of patron.
      [1913 Webster]

   3. The persons who make habitual use of the services of
      another person; one's clients, collectively; as, the
      clientele of a lawyer, doctor, notary, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

clientele
    n 1: customers collectively; "they have an upper class
         clientele" [syn: clientele, patronage, business]