boatswain vs bosun

boatswain and bosun both are nouns.

Word	Noun	Adjective	Verb	Adverb
boatswain	Yes	No	No	No
bosun	Yes	No	No	No

As nouns, boatswain and bosun are synonyms defined as:

boatswain and bosun: a petty officer on a merchant ship who controls the work of other seamen

Other synonyms of boatswain include bo's'n, bo'sun, bos'n.

boatswain (noun)	bosun (noun)
a petty officer on a merchant ship who controls the work of other seamen	a petty officer on a merchant ship who controls the work of other seamen