seed vessel vs epicarp

seed vessel and epicarp both are nouns.

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

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

seed vessel: the ripened and variously modified walls of a plant ovary
epicarp: outermost layer of the pericarp of fruits as the skin of a peach or grape

Other hyponyms of seed vessel include exocarp, mesocarp, endocarp, pit, stone, capsule, bur, burr.

seed vessel (noun)	epicarp (noun)
the ripened and variously modified walls of a plant ovary	outermost layer of the pericarp of fruits as the skin of a peach or grape