sac vs theca

sac and theca both are nouns.

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

As nouns, sac and theca are synonyms defined as:

sac (noun)	theca (noun)
a structure resembling a bag in an animal	outer sheath of the pupa of certain insects
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