covering vs seed vessel

covering and seed vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
covering	Yes	No	No	No
seed vessel	Yes	No	No	No

As nouns, seed vessel is a hyponym of covering; that is, seed vessel is a word with a more specific, narrower meaning than covering:

covering (noun)	seed vessel (noun)
the act of protecting something by covering it	the ripened and variously modified walls of a plant ovary
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