narrow boat vs narrowboat

narrow boat and narrowboat both are nouns.

Word	Noun	Adjective	Verb	Adverb
narrow boat	Yes	No	No	No
narrowboat	Yes	No	No	No

As nouns, narrow boat and narrowboat are synonyms defined as:

narrow boat and narrowboat: a long boat that carries freight and is narrow enough to be used in canals

Other synonyms of narrow boat include canal boat.

narrow boat (noun)	narrowboat (noun)
a long boat that carries freight and is narrow enough to be used in canals	a long boat that carries freight and is narrow enough to be used in canals