thumb
     n 1: the thick short innermost digit of the forelimb [syn: {pollex}]
     2: the part of a glove that provides a covering for the thumb
     3: a convex molding having a cross section in the form of a
        quarter of a circle or of an ellipse [syn: {ovolo}, {quarter
        round}]
     v 1: travel by getting free rides from motorists [syn: {hitchhike},
           {hitch}]
     2: look through a book or other written material; "He thumbed
        through the report"; "She leafed through the volume" [syn:
         {flick}, {flip}, {riffle}, {leaf}, {riff}]
     3: feel or handle with the fingers; "finger the binding of the
        book" [syn: {finger}]
Source: WordNet® 2.0

thumb n. The slider on a window-system scrollbar. So called because
   moving it allows you to browse through the contents of a text window in
   a way analogous to thumbing through a book.


Source: The Jargon File