noun
between-season wear; spring/autumn clothing
Clothing suitable for mild weather, typically worn in spring or autumn when it is neither too hot nor too cold.
春先には薄手の合着が便利です。
Light between-season wear is handy in early spring.
秋の合着をそろそろ出しましょう。
Let's get out the autumn clothing soon.
Refers to the seasonal changing of clothes, while 合着 is the clothing itself worn between seasons.
Compound of 合 (あい, 'between') and 着 (ぎ, 'clothing'), referring to garments worn in the transitional seasons.