Merriam-Webster's Collegiate® Dictionary, 11th Edition
RATCHET
I. noun also rachet see: rock
Date: 1654
a mechanism that consists of a bar or wheel having inclined teeth into which a pawl drops so that motion can be imparted to the wheel or bar, governed, or prevented and that is used in a hand tool (as a wrench or screwdriver) to allow effective motion in one direction only, a pawl or detent for holding or propelling a toothed wheel,
II. verb also rachet
Date: 1972
transitive verb to cause to move by steps or degrees, intransitive verb to proceed by steps or degrees