a piece that is pressed by the thumb, for example on an instrument or on a lid so as to open it
thumbpiece in American English
(ˈθʌmˌpis)
noun
a lever over the hinge on the lid of a tankard, pressed by the thumb to raise the lid
Also called: billet
Word origin
[1750–60; thumb + piece]This word is first recorded in the period 1750–60. Other words that entered Englishat around the same time include: Yankee, permeability, quartz, summation, swish