water cannon vs watercannon

water cannon and watercannon both are nouns.

Word	Noun	Adjective	Verb	Adverb
water cannon	Yes	No	No	No
watercannon	Yes	No	No	No

As nouns, water cannon and watercannon are synonyms defined as:

water cannon and watercannon: a hose (carried on a truck) that fires water under high pressure to disperse crowds (especially crowds of rioters)

water cannon (noun)	watercannon (noun)
a hose (carried on a truck) that fires water under high pressure to disperse crowds (especially crowds of rioters)	a hose (carried on a truck) that fires water under high pressure to disperse crowds (especially crowds of rioters)