safety arch vs strengthener

safety arch and strengthener both are nouns.

Word	Noun	Adjective	Verb	Adverb
safety arch	Yes	No	No	No
strengthener	Yes	No	No	No

As nouns, strengthener is a hypernym of safety arch; that is, strengthener is a word with a broader meaning than safety arch:

safety arch: an undecorated arch that is included in order to strengthen or support a construction
strengthener: a device designed to provide additional strength

Other hypernyms of safety arch include arch, reinforcement.

safety arch (noun)	strengthener (noun)
an undecorated arch that is included in order to strengthen or support a construction	a device designed to provide additional strength