seed vessel vs mesocarp

seed vessel and mesocarp both are nouns.

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

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

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

seed vessel (noun)	mesocarp (noun)
the ripened and variously modified walls of a plant ovary	the middle layer of a pericarp