Source : Webster's Revised Unabridged Dictionary (1913)

Zygospore \Zyg"o*spore\, n. [Gr. ? a yoke + E. spore.] (Bot.)
   (a) Same as {Zygosperm}.
   (b) A spore formed by the union of several zo["o]spores; --
       called also {zygozo["o]spore}.

Source : WordNet®

zygospore
     n : a plant spore formed by two similar sexual cells