Source : Webster's Revised Unabridged Dictionary (1913)

Tetraspore \Tet"ra*spore\, n. [Tetra- + spore.] (Bot.)
   A nonsexual spore, one of a group of four regularly occurring
   in red seaweeds. -- {Tet`ra*spor"ic}, a.

Source : WordNet®

tetraspore
     n : one of the four asexual spores produced within a sporangium