User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-67.86.138.46-20150115070314/@comment-5619706-20150116120527

Both Cas and Death stated Leviathans can kill angles and eat the whole petridish, and that includes archangels.

Similarly, Eve remarked she is older than angels (note the use of the term 'angels') despite talking to Castiel, a Seraph. That means 'angels' were used as a catch-all phrase.