seed vessel vs endocarp

seed vessel and endocarp both are nouns.

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

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

seed vessel: the ripened and variously modified walls of a plant ovary
endocarp: the hard inner (usually woody) layer of the pericarp of some fruits (as peaches or plums or cherries or olives) that contains the seed

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

seed vessel (noun)	endocarp (noun)
the ripened and variously modified walls of a plant ovary	the hard inner (usually woody) layer of the pericarp of some fruits (as peaches or plums or cherries or olives) that contains the seed