Sunday-go-to-meeting clothes

idiomatic plural plural-only

(idiomatic) One's best or most presentable clothes.

Japanese Meaning

特別な場や重要な会議などで着用する、最も整った身なり・衣装

She brought out her Sunday-go-to-meeting clothes for the job interview, even though the office dress code was casual.

彼女は就職の面接のために一張羅を取り出したが、オフィスの服装規定はカジュアルだった。

Sense（1）

(idiomatic) One's best or most presentable clothes.