ball cock vs ballcock

ball cock and ballcock both are nouns.

Word	Noun	Adjective	Verb	Adverb
ball cock	Yes	No	No	No
ballcock	Yes	No	No	No

As nouns, ball cock and ballcock are synonyms defined as:

ball cock and ballcock: floating ball that controls level in a water tank

ball cock (noun)	ballcock (noun)
floating ball that controls level in a water tank	floating ball that controls level in a water tank