theca vs sac

theca and sac both are nouns.

Word	Noun	Adjective	Verb	Adverb
theca	Yes	No	No	No
sac	Yes	No	No	No

As nouns, theca and sac are synonyms defined as:

theca (noun)	sac (noun)
outer sheath of the pupa of certain insects	a structure resembling a bag in an animal
a case or sheath especially a pollen sac or moss capsule	a case or sheath especially a pollen sac or moss capsule
	an enclosed space