Definition of "thumb" in English

noun

1. The shortest and thickest 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.

2. (graphical user interface) The part of a slider that may be moved linearly along the slider.

   • a scroll-bar thumb

3. (colloquial, Internet) A thumbnail picture.

4. A top hatch plate for covering an excavator bucket, used to keep material in the digger bucket after scooping it up, and not letting it spill out.

verb

1. (transitive) To touch or cover with the thumb.

   • to thumb the touch-hole of a cannon

2. (transitive, with through) To turn the pages of (a book) in order to read it cursorily.

   • thumb through
   • I thumbed through the book and decided not to bother reading it all.

3. (travel) To hitchhike.

   • So I started thumbin' back east, toward my hometown.

4. To soil or wear with the thumb or the fingers; to soil, or wear out, by frequent handling.

5. To manipulate (an object) with the thumb; especially, to pull back the hammer or open the cylinder of a revolver.

6. To fire (a single action revolver) quickly by pulling the hammer while keeping the trigger depressed.