The Collaborative International Dictionary of English v.0.48:

Soupcon \Soup`[,c]on"\, n. [F.]
   A suspicion; a suggestion; hence, a very small portion; a
   taste; as, coffee with a soup[,c]on of brandy; a soup[,c]on
   of coquetry.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

soupcon
    n 1: a slight but appreciable amount; "this dish could use a
         touch of garlic" [syn: touch, hint, tinge, mite,
         pinch, jot, speck, soupcon]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "soupcon":
   cast, dash, gleam, hint, idea, infusion, inkling, intimation, lick,
   look, sauce, scintilla, seasoning, shade, shadow, sip, smack,
   smattering, smell, spark, spice, sprinkling, streak, suggestion,
   sup, suspicion, taint, taste, tempering, thought, tinct, tincture,
   tinge, tint, touch, trace, vestige, whiff