rivet vs soak up

rivet is a noun but soak up is not a noun.

Word	Noun	Adjective	Verb	Adverb
rivet	Yes	No	Yes	No
soak up	No	No	Yes	No

As verbs, soak up is a hyponym of rivet; that is, soak up is a word with a more specific, narrower meaning than rivet:

Other hyponyms of rivet include absorb, engross, engulf, immerse, plunge, steep, recall, think, zoom in, hear, listen, take heed.

rivet (noun)	soak up (noun)
heavy pin having a head at one end and the other end being hammered flat after being passed through holes in the pieces that are fastened together
ornament consisting of a circular rounded protuberance (as on a vault or shield or belt)

rivet (verb)	soak up (verb)
direct one's attention on something	devote (oneself) fully to
hold (someone's attention)	take in, also metaphorically
fasten with a rivet or rivets