stutter

Concise Oxford English Dictionary © 2008 Oxford University Press:
stutter/ˈstʌtə(r)/

▶verb talk with continued involuntary repetition of sounds, especially initial consonants.

■ (of a machine or gun) produce a series of short, sharp sounds.

▶noun a tendency to stutter while speaking.

– derivatives
stutterer noun,
stuttering adjective,
stutteringly adverb.

– origin C16: frequentative of dial. stut, of Gmc origin.