tie down vs constrain

tie down and constrain both are verbs.

Word	Noun	Adjective	Verb	Adverb
tie down	No	No	Yes	No
constrain	No	No	Yes	No

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

tie down: secure with or as if with ropes
constrain: to close within bounds, or otherwise limit or deprive of free movement

Other hypernyms of tie down include confine, hold, restrain.

tie down (verb)	constrain (verb)
restrain from independence by an obligation	severely restrict in scope or extent
secure with or as if with ropes	to close within bounds, or otherwise limit or deprive of free movement
	compel to behave in a certain way