The Collaborative International Dictionary of English v.0.48:

Nicker \Nick"er\, n. [From Nick, v. t.]
   1. One of the night brawlers of London formerly noted for
      breaking windows with half-pence. [Cant] --Arbuthnot.
      [1913 Webster]

   2. The cutting lip which projects downward at the edge of a
      boring bit and cuts a circular groove in the wood to limit
      the size of the hole that is bored.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nicker
    n 1: the characteristic sounds made by a horse [syn: neigh,
         nicker, whicker, whinny]
    v 1: make a characteristic sound, of a horse [syn: neigh,
         nicker, whicker, whinny]