stutter

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive & transitive verb To speak or utter with a spasmodic repetition or prolongation of sounds.
• noun The act or habit of stuttering.

from The Century Dictionary.

• noun One who stuts or stutters; a stutterer.
• noun A marked stammer; broken and hesitating utterance of words.
• To speak with a marked stammer; utter words with frequent breaks and repetitions of parts, either habitually or under special excitement.
• Synonyms Falter, etc. See stammer.
• To utter with breaks and repetitions of parts of words; say disjointedly.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of stuttering; a stammer. See stammer, and stuttering.
• noun obsolete One who stutters; a stammerer.
• verb To hesitate or stumble in uttering words; to speak with spasmodic repetition or pauses; to stammer.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive To speak with a spasmodic repetition of vocal sounds.
• noun A speech disorder characterised by stuttering.
• noun obsolete One who stutters; a stammerer.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb speak haltingly
• noun a speech disorder involving hesitations and involuntary repetitions of certain sounds