The Collaborative International Dictionary of English v.0.48:

Neap \Neap\ (n[=e]p), a. [As. n[=e]pfl[=o]d neap flood; cf.
   hnipian to bend, incline.]
   Low.
   [1913 Webster]

   Neap tides, the lowest tides of the lunar month, which
      occur in the second and fourth quarters of the moon; --
      opposed to spring tides.
      [1913 Webster]