ETYM French froc a monk's cowl, coat, garment, Late Lat. frocus, froccus, flocus, floccus, from Latin floccus a flock of wool; hence orig., a flocky cloth or garment; cf. Latin flaccus flabby, Eng. flaccid.
1. A loose outer garment; especially, a gown forming a part of early modern clothing for women and children.
2. A coarse gown worn by monks or friars, and supposed to take the place of all, or nearly all, other garments.

To put a frock on.