Rare, formal noun referring to a state of decline or decay, often of institutions, fortunes, or physical condition. Not in common modern use; 衰退 (すいたい) or 衰微 (すいび) are more frequent.
The decline of that country was obvious to everyone.
Composed of 衰 (decline, weaken) and 幣 (originally 'offering' or 'currency', here likely used for its sense of 'worn out' or 'spent'). The exact historical derivation is uncertain; the compound is rare and may be a learned formation.