forestay vs mainstay

forestay and mainstay both are nouns.

Word	Noun	Adjective	Verb	Adverb
forestay	Yes	No	No	No
mainstay	Yes	No	No	No

As nouns, mainstay is a hyponym of forestay; that is, mainstay is a word with a more specific, narrower meaning than forestay:

forestay: an adjustable stay from the foremast to the deck or bowsprit; controls the bending of the mast
mainstay: the forestay that braces the mainmast

Other hyponyms of forestay include headstay.

forestay (noun)	mainstay (noun)
an adjustable stay from the foremast to the deck or bowsprit; controls the bending of the mast	the forestay that braces the mainmast
	a central cohesive source of support and stability
	a prominent supporter