sit down vs hunker down

sit down and hunker down both are verbs.

Word	Noun	Adjective	Verb	Adverb
sit down	No	No	Yes	No
hunker down	No	No	Yes	No

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

sit down: be in a position in which one's upper body is largely upright and supported by one's backside
hunker down: sit on one's heels

Other hyponyms of sit down include lounge, sprawl, perch, rest, roost, crouch, hunker, scrunch, scrunch up, squat.

sit down (verb)	hunker down (verb)
show to a seat; assign a seat for	hold stubbornly to a position
be in a position in which one's upper body is largely upright and supported by one's backside	sit on one's heels
take a seat	take shelter