falter
v.v. to lose your strength or confidence, or to speak in a way that is not steady or clear.
v. to lose strength, confidence, or steadiness; to speak in an uncertain or hesitant manner.
His voice began to falter as he told the story.
The runner's legs began to falter in the final lap, but she managed to cross the finish line.
As the evidence against him mounted, the suspect's confidence began to falter, leading to a series of increasingly incoherent statements during the interrogation.
From Middle English falteren (“to stagger; be unsteady, tremble, quiver; to stammer; be entangled, get caught”), further origin unknown. Probably from a North Germanic source such as Old Norse faltrask (“to hesitate, be puzzled, be encumbered”). May also be a frequentative of fold, although the change from d to t is unusual.