1. noun /θʌm/
a) The short thick digit of the hand that for humans has the most mobility and can be made to oppose (moved to touch) all of the other fingers.
b) The part of a slider that may be moved linearly along the slider.
2. verb /θʌm/
a) To touch with the thumb.
I thumbed through the book and decided not to bother reading it all.
b) To turn the pages of (a book) in order to read it cursorily.
So I started thumbin back east, toward my hometown.
Wikipedia foundation.