The Collaborative International Dictionary of English v.0.48:

pectin \pec"tin\ (p[e^]k"t[i^]), n. [Gr. phkto`s curdled,
   congealed, from phgny`nai to make fast or stiff: cf. F.
   pectine.] (Chem.)
   One of a series of carbohydrates, commonly called vegetable
   jelly, found very widely distributed in the vegetable
   kingdom, especially in ripe fleshy fruits, as apples,
   cranberries, etc. It is extracted as variously colored,
   translucent substances, which are soluble in hot water but
   become viscous on cooling. It is commonly used in making
   fruit jelllies.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pectin
    n 1: any of various water-soluble colloidal carbohydrates that
         occur in ripe fruit and vegetables; used in making fruit
         jellies and jams