i-adjective
somewhat cold; a bit chilly
Describes a mild, slightly uncomfortable coldness, often of weather or air. Softer than 寒い.
朝晩は薄寒くなってきた。
Mornings and evenings have become a bit chilly.
薄寒い風が吹いている。
A somewhat cold wind is blowing.
寒い means 'cold' in a general sense, while 薄寒い specifically indicates a mild, slight coldness.
Compound of 薄 (usu-, 'light, weak') + 寒い (samui, 'cold'). The reading うすざむい is a voiced variant (rendaku) of うすさむい.