restrain vs tie down

restrain and tie down both are verbs.

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

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

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

Other hyponyms of restrain include bind, tie up, truss, fetter, shackle, enchain, pinion, shackle, impound, pound, pound, pound up, fold, pen up, ground.

restrain (verb)	tie down (verb)
prevent the action or expression of	restrain from independence by an obligation
to close within bounds, or otherwise limit or deprive of free movement	secure with or as if with ropes
restrict (someone or something) so as to make free movement difficult
prevent (someone or something) from doing something