Definitions of thumb:

• noun:   the part of a glove that provides a covering for the thumb
• noun:   the thick short innermost digit of the forelimb
• noun:   a convex molding having a cross section in the form of a quarter of a circle or of an ellipse
• verb:   feel or handle with the fingers
• verb:   look through a book or other written material

  Example: "He thumbed through the report"

• verb:   travel by getting free rides from motorists