Emily Dickinson Lexicon

BAL'LAST, n. [Sax. bat, a boat, with last, a load; D. Ger. and Dan. last; W. llwyth; Arm. lastr, a load; bat-last, boat-load, corrupted into ballast; Russ. ballast; Fr. lest; Sp. lastre; Sax. hlæstan, to load a ship.]

1. Heavy matter, as stone, sand or iron, laid on the bottom of a ship or other vessel, to sink it in the water to such a depth, as to enable it to carry sufficient sail, without oversetting. Shingle ballast, is ballast of coarse gravel. – Mar. Dict.
2. Figuratively, that which is used to make a thing steady. – Swift.