'Frock coat' definitions:

Definition of 'frock coat'

noun

A man's coat having knee-length skirts front and back; worn in the 19th century

From: GCIDE

Frock \Frock\ (fr[o^]k), n. [F. froc a monk's cowl, coat, garment, LL. frocus, froccus, flocus, floccus, fr. L. floccus a flock of wool; hence orig., a flocky cloth or garment; cf. L. flaccus flabby, E. flaccid.]
1. A loose outer garment; especially, a gown forming a part of European modern costume for women and children; also, a coarse shirtlike garment worn by some workmen over their other clothes; a smock frock; as, a marketman's frock. [1913 Webster]
2. A coarse gown worn by monks or friars, and supposed to take the place of all, or nearly all, other garments. It has a hood which can be drawn over the head at pleasure, and is girded by a cord. [1913 Webster]
Frock coat, a body coat for men, usually double-breasted, the skirts not being in one piece with the body, but sewed on so as to be somewhat full.
Smock frock. See in the Vocabulary. [1913 Webster]