The Collaborative International Dictionary of English v.0.48:

Snaffle \Snaf"fle\, n. [D. snavel a beak, bill, snout; akin to
   G. schnabel, OHG. snabul,. sneb, snebbe, OFries. snavel
   mouth, Dan. & Sw. snabel beak, bill, Lith. snapas, and to E.
   snap, v. See Snap, and cf. Neb.]
   A kind of bridle bit, having a joint in the part to be placed
   in the mouth, and rings and cheek pieces at the ends, but
   having no curb; -- called also snaffle bit.
   [1913 Webster]

WordNet (r) 3.0 (2006):

snaffle bit
    n 1: a simple jointed bit for a horse; without a curb [syn:
         snaffle, snaffle bit]