falter

Short definition from Wiktionary

Noun

1. 1
   An unsteadiness.

Verb

1. 1
   To waver or be unsteady; to weaken or trail off.
2. 2
   To stammer; to utter with hesitation, or in a weak and trembling manner.
3. 3
   To fail in distinctness or regularity of exercise; said of the mind or of thought.
4. 4
   To stumble.
5. 5
   To lose faith or vigor; to doubt or abandon (a cause).
6. 6
   To hesitate in purpose or action.
7. 7
   To cleanse or sift, as barley.