a large wooden box built to God's instructions: either Noah's vessel or the gold covered chest that held the covenant
In ordinary Greek this was an unremarkable word. It named a box: a chest, a coffer, a strongbox, the sort of thing you kept valuables or documents in. Nothing in the word itself means "ship," and nothing in it means "holy." Its weight in the New Testament comes entirely from the two objects it happens to name.
Both of those objects are containers someone built because God gave the specifications:
- Noah's vessel, a wooden box big enough to carry his household and the animals through the flood
- the gold covered chest in Israel's sanctuary, which held the tablets of the covenant
The two never blur in practice, because the surrounding words always make the object plain. Four of the six occurrences sit inside the flood story, and the other two name the covenant outright. So one plain Greek noun stretches across a boat sized vessel and a piece of sanctuary furniture, and English follows with a single word, "ark," borrowed from the Latin word for a chest.
The choice of word is quietly informative. Greek had a perfectly good term for a boat (πλοῖον), and the New Testament uses it constantly for the fishing craft on the lake and for ships at sea. It is never applied to Noah's vessel. What Noah built is described as a box that floated, not as a ship he sailed.