silt vs back up

silt is a noun but back up is not a noun.

Word	Noun	Adjective	Verb	Adverb
silt	Yes	No	Yes	No
back up	No	No	Yes	No

As verbs, back up is a hypernym of silt; that is, back up is a word with a broader meaning than silt:

Other hypernyms of silt include choke, choke off, clog, clog up, congest, crap up, foul.

silt (noun)	back up (noun)
mud or clay or small rocks deposited by a river or lake

silt (verb)	back up (verb)
become chocked with silt	establish as valid or genuine
	become or cause to become obstructed
	make a copy of (a computer file) especially for storage in another place as a security copy
	move backwards from a certain position
	give moral or psychological support, aid, or courage to