The thumb is the short finger on your hand that is nearest your wrist.(noun)
The short finger on your hand that is opposable to your other fingers is an example of a thumb.
To thumb is to use the short finger of your hand to touch something or to turn the pages of a book.(verb)
When you turn the pages of a book using the short finger on your hand, this is an example of a time when you thumb through the book.
See thumb in Webster's New World College Dictionary
Origin: ME (with unhistoric -b) < OE thuma, akin to Ger daume(n) < IE base *tēu-, to swell, increase > L tumor: basic sense, “enlarged finger”
See thumb in American Heritage Dictionary 4
Origin: Middle English
Origin: , from Old English thūma; see teuə- in Indo-European roots.
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