stammering

Apt to stammer; hesitating in speech; stuttering. -- Stam·mer·ing·ly, adv.

Stam·mer·ing
n.

(Physiol.) A disturbance in the formation of sounds. It is due essentially to long-continued spasmodic contraction of the diaphragm, by which expiration is prevented, and hence it may be considered as a spasmodic inspiration.

noun

A speech impediment marked by involuntary repetitions and pauses: stammer, stutter, stuttering. See words.

The adjective has one meaning:

Meaning #1: unable to speak freely and easily
  Synonym: stuttering