slow down vs modify

slow down and modify both are verbs.

Word	Noun	Adjective	Verb	Adverb
slow down	No	No	Yes	No
modify	No	No	Yes	No

As verbs, modify is a hypernym of slow down; that is, modify is a word with a broader meaning than slow down:

Other hypernyms of slow down include alter, change.

slow down (verb)	modify (verb)
become less tense, rest, or take one's ease	make less severe or harsh or extreme
lose velocity; move more slowly	add a modifier to a constituent
become slow or slower	cause to change; make different; cause a transformation
reduce the speed of
cause to proceed more slowly