Arca, arcus & arx

The three nouns arca, arcus and arx make an interesting little set of partial homophones.  Arca, ae (f) is first declension and means: box, moneybox / purse.  Arcus, -us (m) is fourth declension and means: bow, rainbow, arch, arc.  Arx, arcis (f) is third declension and means: stronghold, summit.  We have several English words from arca and arcus: arc, arch, ark (as in Noah's Ark and Ark of the Covenant).