The Collaborative International Dictionary of English v.0.48:

Affricate \Af"fri*cate\, n. [L. affricatus, p. p. of affricare
   to rub against; af- = ad- + fricare to rub.] (Phon.)
   A combination of a stop, or explosive, with an immediately
   following fricative or spirant of corresponding organic
   position, as pf in german Pfeffer, pepper, z (= ts) in German
   Zeit, time.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

affricate
    n 1: a composite speech sound consisting of a stop and a
         fricative articulated at the same point (as `ch' in `chair'
         and `j' in `joy') [syn: affricate, affricate consonant,
         affricative]