ecu n.

"shield on which a coat of arms is depicted," late 15c., from Old North French escuchon, variant of Old French escusson "half-crown (coin); coat of arms, heraldic escutcheon," from Vulgar Latin *scutionem, from Latin scutum "shield," from PIE *skoito- "piece of wood, sheath, shield" (source also of Old Irish sciath, Welsh ysgwyd, Breton scoed "shield;" Old Prussian staytan "shield;" Russian ščit "shield"), probably a noun derivative of a variant of PIE root *skei- "to cut, split," on the notion of "board."

Escutcheon of pretense, in her., a small escutcheon charged upon the main escutcheon, indicating the wearer's pretensions to some distinction, or to an estate, armorial bearings, etc., which are not his by strict right of descent. It is especially used to denote the marriage of the bearer to an heiress whose arms it bears. Also called inescutcheon. [Century Dictionary]

Clev. Without doubt: he is a Knight?

Jord. Yes Sir.

Clev. He is a Fool too?

Jord. A little shallow[,] my Brother writes me word, but that is a blot in many a Knights Escutcheon.

[Edward Ravenscroft, "Mamamouchi, or the Citizen Turn'd Gentleman," 1675]

Spanish and Portuguese coin, 1821, from Spanish/Portuguese escudo, from Latin scutum "a shield" (see escutcheon). Also compare ecu.