pinniped vs walrus

pinniped and walrus both are nouns.

Word	Noun	Adjective	Verb	Adverb
pinniped	Yes	No	No	No
walrus	Yes	No	No	No

As nouns, walrus is a hyponym of pinniped; that is, walrus is a word with a more specific, narrower meaning than pinniped:

pinniped: aquatic carnivorous mammal having a streamlined body specialized for swimming with limbs modified as flippers
walrus: either of two large northern marine mammals having ivory tusks and tough hide over thick blubber

Other hyponyms of pinniped include seal, sea horse, seahorse.

pinniped (noun)	walrus (noun)
aquatic carnivorous mammal having a streamlined body specialized for swimming with limbs modified as flippers	either of two large northern marine mammals having ivory tusks and tough hide over thick blubber