ballast
n.heavy material like sand or iron that people put in the bottom of a ship to keep it steady. It helps the boat stay balanced and upright in the water.
n.heavy substance, such as water, sand, or iron, placed in the hold of a vessel or the base of a structure to provide stability. Often used metaphorically to describe something that provides mental or emotional steadiness.
“The ship took on water as ballast to stay stable.”
“Without enough ballast in the lower hull, the tall ship would be at risk of tipping over in high winds.”
“The captain ordered the crew to discharge the water ballast as the vessel entered the shallower waters of the estuary to reduce its draft.”
Usually uncountable when referring to the material itself; can be used as a modifier in phrases like 'ballast tank'.
“Originally native to the Black and Caspian seas, round goby arrived in the Great Lakes in the early 1990s in cargo ships' ballast.”
“These sacs act much like the ballast tanks of a submarine.”
From Middle English bar (“bare”) + last (“load”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.