Source : Webster's Revised Unabridged Dictionary (1913)

Stammering \Stam"mer*ing\, a.
   Apt to stammer; hesitating in speech; stuttering. --
   {Stam"mer*ing*ly}, adv.

Source : WordNet®

stammeringly
     adv : with a stammer; "`Will you marry me?' he asked stammeringly"
           [syn: {stutteringly}]