the part of a glove that provides a covering for the thumb
"He bought a new pair of work gloves specifically to protect his thumbs from cuts and abrasions."
a convex molding having a cross section in the form of a quarter of a circle or of an ellipse
"The carpenter smoothed the rounded edge on the wooden post to create a thumb that would be comfortable against his knee."
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.
"The thumb is the only finger on your hand that can be moved to touch the tips of your other four digits."
In plain English: A thumb is your short, thick finger on each hand that doesn't have an opposite finger to touch it with.
"He gave me a thumbs-up to show he agreed with my plan."
Usage: Use this word when referring specifically to the shortest, thickest finger on your hand capable of touching its neighbors. As a verb, it means to press against something using that digit rather than just placing an object in your palm.
To touch or cover with the thumb.
"She held the pen between her fingers and pressed it firmly against the page with her thumb."
In plain English: To thumb means to quickly flip through pages of something by sliding your thumb over them.
"I will thumb through these pages to see if I can find that story."
The word "thumb" comes from Old English þūma, which originally meant the same thing. It ultimately traces back to a Proto-Indo-European root meaning "to grow."