Source : Webster's Revised Unabridged Dictionary (1913)

Ratch \Ratch\, n. (Zo["o]l.)
   Same as {Rotche}.

Ratch \Ratch\, n. [See {Rack} the instrument, {Ratchet}.]
   A ratchet wheel, or notched bar, with which a pawl or chick
   works.

Source : WordNet®

ratch
     n : mechanical device consisting of a toothed wheel or rack
         engaged with a pawl that permits it to move in only one
         direction [syn: {ratchet}, {rachet}]