truss vs tie down

truss is a noun but tie down is not a noun.

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

As verbs, truss and tie down are synonyms defined as:

Other synonyms of truss include bind, tie up.

truss (noun)	tie down (noun)
a framework of beams (rafters, posts, struts) forming a rigid structure that supports a roof or bridge or other structure
(medicine) a bandage consisting of a pad and belt; worn to hold a hernia in place by pressure
(architecture) a triangular bracket of brick or stone (usually of slight extent)

truss (verb)	tie down (verb)
support structurally	restrain from independence by an obligation
tie the wings and legs of a bird before cooking it	secure with or as if with ropes
secure with or as if with ropes