The Collaborative International Dictionary of English v.0.48:

Sennit \Sen"nit\, n. [Seven + knit.]
   1. (Naut.) A braided cord or fabric formed by plaiting
      together rope yarns or other small stuff.
      [1913 Webster]

   2. Plaited straw or palm leaves for making hats.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sennit
    n 1: flat braided cordage that is used on ships