Definition of "Thumb" :
noun: a convex molding having a cross section in the form of a quarter of a circle or of an ellipse
noun: the part of a glove that provides a covering for the thumb
noun: the thick short innermost digit of the forelimb
verb: feel or handle with the fingers
verb: travel by getting free rides from motorists
verb: look through a book or other written material
"He thumbed through the report."