Ratchet :: Ratchet (n.) A pawl, click, or detent, for holding or propelling a ratchet wheel, or ratch, etc..
Ratchet :: Ratchet (n.) A mechanism composed of a ratchet wheel, or ratch, and pawl. See Ratchet wheel, below, and 2d Ratch..
Scratcher :: Scratcher (n.) One who, or that which, scratches; specifically (Zool.), any rasorial bird..