capella, n. — Green’s Dictionary of Slang

capella n.

[Lat. cappella, little cloak or cape, ult. f. cappella or cloak of St Martin, preserved by the Frankish kings as a sacred relic, carried into battle, and used to give sanctity to oaths. The name was then applied to the sanctuary in which the relic was preserved under the care of its cappellani (chaplains), and thence to any sanctuary containing holy relics and thus to any place used for worship, other than a church, the earlier name for which was oratorium, the oratory]

1. an overcoat.

1937–84

Partridge DSUE (1984) 181/1: C.19–20 obs.

2. (Polari) a (small) cap.

2019		P. Baker Fabulosa 290/1: capella, capolla, capelli, kapella a hat or cap.
2023		R. Milward Man-Eating Typewriter 129: Joshed up to the nobbas in his [...] bulbous Phrygian capella.