Formal term for a missing part, gap, or deficiency, often used in legal, academic, or technical contexts. Not an everyday word.
There is an important gap in this contract.
New regulations were established to fill the lacuna in the law.
invalid coupon
Compound of 欠 (lack) and 缺 (lack, gap), both meaning absence or deficiency. The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning of a gap or missing element.