Definitions of stumble:

• noun:   an unsteady uneven gait
• noun:   an unintentional but embarrassing blunder
• verb:   encounter by chance

  Example: "I stumbled across a long-lost cousin last night in a restaurant"

• verb:   make an error
• verb:   miss a step and fall or nearly fall

  Example: "She stumbled over the tree root"

• verb:   walk unsteadily

  Example: "The drunk man stumbled about"