Rare term for a male sheep; in modern Japanese 牡羊 (おひつじ) is far more common. The cross-reference to 牡羊 confirms this is the same animal.
See also: 牡羊
In old texts, the notation 羝羊 sometimes refers to a male sheep.
person who lives by instinct
Idiomatic and rare; describes someone who acts on impulse or base desires rather than reason. Likely derived from the image of a ram as a creature of instinct.
He lives entirely by instinct, just like a ram.