endospore (n.)

word-forming element meaning "inside, within, internal," from Greek endon "in, within" (from PIE *en-do-, extended form of root *en "in").

"reproductive body in flowerless plants corresponding to the seeds of flowering ones," 1836, from Modern Latin spora, from Greek spora "a seed, a sowing, seed-time," related to sporas "scattered, dispersed," sporos "a sowing," from PIE *spor-, variant of root *sper- "to spread, sow" (see sparse).