theca vs covering

theca and covering both are nouns.

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

As nouns, covering is a hypernym of theca; that is, covering is a word with a broader meaning than theca:

Other hypernyms of theca include cover, natural covering.

theca (noun)	covering (noun)
outer sheath of the pupa of certain insects	the act of protecting something by covering it
a case or sheath especially a pollen sac or moss capsule	the work of applying something
	the act of concealing the existence of something by obstructing the view of it
	an artifact that covers something else (usually to protect or shelter or conceal it)
	a natural object that covers or envelops