From Longman Dictionary of Contemporary Englishbelly buttonˈbelly ˌbutton noun [countable] informal HBHthe small round mark in the middle of your stomach SYN navel
Examples from the Corpus
belly button• A man with monogrammed shirts, a maid, a mansion, and all he wanted was to finger her belly button.• The ruby in her belly button stayed put.• His checked shirt was pulled out of his pants, and his belly button was showing.• In the early 1960s and 1970s and in the mid 1990s shrunken tight clothing often exposed the belly button.• The belly button was protruding and it looked ready to burst. 