slow down vs sit back

slow down and sit back both are verbs.

Word	Noun	Adjective	Verb	Adverb
slow down	No	No	Yes	No
sit back	No	No	Yes	No

As verbs, sit back is a hyponym of slow down; that is, sit back is a word with a more specific, narrower meaning than slow down:

Other hyponyms of slow down include veg out, vegetate, take it easy.

slow down (verb)	sit back (verb)
become less tense, rest, or take one's ease	settle into a comfortable sitting position
lose velocity; move more slowly	be inactive or indifferent while something is happening
become slow or slower
reduce the speed of
cause to proceed more slowly