Yes you are right that cove is a noun and its meaning is a small inlet or small cave in the mountain. It can be also used as a verb as coving, which means to make or become a cove. As it is a noun therefore, its antonym is not available, however, I had gone through a synonyms and antonyms database which gives some antonyms of Cove but I do not believe on them because English dictionary does not give any antonym of cove as a noun.
Synonyms and antonyms database
Synonyms and antonyms database