The Collaborative International Dictionary of English v.0.48:

Thatch \Thatch\, v. t. [imp. & p. p. Thatched; p. pr. & vb. n.
   Thatching.] [From Thatch, n.: cf. OE. thecchen, AS.
   ?eccean to cover.]
   To cover with, or with a roof of, straw, reeds, or some
   similar substance; as, to thatch a roof, a stable, or a stack
   of grain.
   [1913 Webster]