Source : Webster's Revised Unabridged Dictionary (1913)

Lammas \Lam"mas\, n. [AS. hl[=a]mmesse, hl[=a]fm[ae]sse, loaf
   mass, bread feast, or feast of first fruits; hl[=a]f loaf +
   m[ae]sse mass. See {Loaf}, and {Mass} religious service.]
   The first day of August; -- called also {Lammas day}, and
   {Lammastide}.

Source : WordNet®

Lammastide
     n : the season of Lammas