callback vs request

callback and request both are nouns.

Word	Noun	Adjective	Verb	Adverb
callback	Yes	No	No	No
request	Yes	No	Yes	No

As nouns, request is a hypernym of callback; that is, request is a word with a broader meaning than callback:

callback: a request by the manufacturer of a defective product to return the product (as for replacement or repair)
request: the verbal act of requesting

Other hypernyms of callback include asking.

callback (noun)	request (noun)
a request by the manufacturer of a defective product to return the product (as for replacement or repair)	the verbal act of requesting
	a formal message requesting something that is submitted to an authority

callback (verb)	request (verb)
	express the need or desire for
	ask (a person) to do something
	inquire for (information)