The word かのしし appears in old texts as a term for deer.
Archaic/poetic kanji spelling for かのしし. In modern Japanese, 鹿 is normally read しか.
Kanji spelling explicitly for 'venison' sense, but the reading かのしし itself is archaic/poetic.
The exact derivation is uncertain. かのしし is an old Japanese word for deer/venison, later largely replaced by しか.