spec. Originally designating the distinctive long coat made of motley which was worn by a fool in the late 16th and early 17th centuries; in later…

In the sense ‘pertaining to, forming (part of) a uniform’, as uniform case, uniform clothes, uniform coat.

characteristic of a groom, like that of a groom.

Designating clothing worn by or associated with a preacher or minister; (also) designating clothing resembling this in style; as come-to-Jesus coat…

Of articles of attire: somewhat informal or casual.

Of clothes: suitable for informal wear. (Cf. B. 4.)

attributive. Originally and chiefly U.S. Designating an article or suit of loose-fitting clothing, usually made of cotton or other washable fabric…