The Collaborative International Dictionary of English v.0.48:

Ratch \Ratch\ (r[a^]ch), n. (Zool.)
   Same as Rotche.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ratch \Ratch\ (r[a^]ch), n. [See Rack the instrument,
   Ratchet.]
   A ratchet wheel, or notched bar, with which a pawl or click
   works.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ratch
    n 1: 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, ratch]