Lacuna
Etymology
Latin "lacuna" meant a pit, hollow, or pool, from "lacus," lake. Scholars adopted it for the blank left where a manuscript is damaged or a word is lost. The same "lacus" gives English "lake" and "lagoon."
noun · /luh-KYOO-nuh/
A gap or missing portion, especially a hole in a text, argument, or body of knowledge.
What it names
An absence, precisely — not just something missing, but a defined blank where something should be.
Example
The statute had a lacuna the lawyers exploited: it never said what happened if both parties died at once.
Related idea
A specialized cousin of hiatus, a gap in continuity; it shares its watery root, "lacus," with lagoon.