arca

Arca, arcae, f., first declension, from arceo, "shut in, keep off". The idea is a container that keeps things in and other people out, so the classical arca is a strongbox: a rich man's arca is effectively his bank balance, and "ex arca solvere" is to pay in cash. It also serves for a coffin, and for the box a prisoner was shut into.

The Vulgate is what fixes the word for this corpus. Arca renders both Noah's ark and the Ark of the Covenant, arca Noe and arca foederis, which is where English ark comes from and why the church Latin sense is overwhelmingly sacred rather than financial. A learner meeting arca in a medieval charter should still read strongbox first; monasteries kept their money somewhere.