Regarding the use of the Chinese characters "蝦夷," one theory asserts that the people had some sort of name related to the sound "kai" (the Ainu were called "kui" by Mongolians and "kuriru" by Russians), and another asserts that the people had long beards and therefore resembled a prawn (蝦) or a lobster.
蝦夷については、カイという音（アイヌ人はモンゴル人から「クイ」ロシア人からは「クリル」と呼ばれた）に通じる呼び名があったためとも、蝦（エビ）に似て髭が長かったためだとも推測される。