Bulgarian Хлебен [khlébenAdj. An otherwise juicy fruit that's too dry and unpleasant to eat, making you feel like you're eating bread.

It literally means 'breadsy'. Тази диня е хлебна = this watermelon is breadsy = it's overripe and lost its juiciness. You know how such fruits have this crumb-like texture that makes them off putting. I think that's where the word comes from.