The term 'Ancient Couples Carrier' is a reference to the biblical story of Noah's ARK. Noah was instructed by God to build an ARK and fill it with two of every kind of animal, as well as his family, in order to survive a great flood. The ARK was the vessel that carried Noah and his family, as well as the animals, through the flood. Therefore, the crossword solution for this term is ARK, which is a three-letter word.