noun
living under heaven; one's earthly existence
Literary or formal noun referring to the state of being alive in this world, often used in the set phrase 戴天の仇 (a mortal enemy one cannot live under the same sky with). Rarely used outside fixed expressions.
彼は父の敵を戴天の仇と見なしていた。
He regarded his father's enemy as a mortal foe he could not share the sky with.
「戴天」は、現代ではほとんど「戴天の仇」という決まった言い回しでしか見かけない。
In modern Japanese, 戴天 is almost only seen in the fixed expression 戴天の仇.
From Chinese 戴天 (dàitiān), literally 'to carry the sky on one's head', meaning to live under heaven. The exact historical derivation is uncertain; the spelling is conventionally associated with this meaning.