headstay vs forestay

headstay and forestay both are nouns.

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

As nouns, forestay is a hypernym of headstay; that is, forestay is a word with a broader meaning than headstay:

headstay: the farthest forward forestay that runs from the bow or bowsprit to the top of the mast.
forestay: an adjustable stay from the foremast to the deck or bowsprit; controls the bending of the mast

headstay (noun)	forestay (noun)
the farthest forward forestay that runs from the bow or bowsprit to the top of the mast.	an adjustable stay from the foremast to the deck or bowsprit; controls the bending of the mast