corncob vs corn cob

corncob and corn cob both are nouns.

Word	Noun	Adjective	Verb	Adverb
corncob	Yes	No	No	No
corn cob	Yes	No	No	No

As nouns, corncob and corn cob are synonyms defined as:

corncob and corn cob: the hard cylindrical core that bears the kernels of an ear of corn

corncob (noun)	corn cob (noun)
the hard cylindrical core that bears the kernels of an ear of corn	the hard cylindrical core that bears the kernels of an ear of corn