stumble

Concise Oxford English Dictionary © 2008 Oxford University Press:
stumble/ˈstʌmbl/

▶verb

• 1 trip or momentarily lose one's balance.

  ■ walk unsteadily.

• 2 make a mistake or repeated mistakes in speaking.

• 3 (stumble across/on/upon) find by chance.

▶noun an act of stumbling.

– derivatives
stumbler noun,
stumbling adjective,
stumblingly adverb.

– origin ME: from ON, from the Gmc base of stammer.