falter (v.)

late 14c., "to stagger, totter," of unknown origin, possibly from a Scandinavian source (compare Old Norse faltrask "be burdened, hesitate, be troubled"), or else a frequentative of Middle English falden "to fold," influenced by fault (but OED rejects any direct connection to that word). Of the tongue, "to stammer," mid-15c. Related: Faltered; faltering.