Source : Webster's Revised Unabridged Dictionary (1913)

Sneeringly \Sneer"ing*ly\, adv.
   In a sneering manner.

Source : WordNet®

sneeringly
     adv : with a sneer; in an uncomplimentary sneering manner; "`I
           don't believe in these customs,' he said sneeringly"
           [syn: {superciliously}, {snidely}]