Noun

The state of not existing.

The nonexistence of Father Christmas and the Tooth Fairy came as something of a shock .

Noun

(uncountable) Inadequacy or incompleteness.

* {{quote-book, year=1963, author=(Margery Allingham), title=(The China Governess)

, chapter=17 citation , passage=The face which emerged was not reassuring. […]. He was not a mongol but there was a deficiency of a sort there, and it was not made more pretty by a latter-day hair cut which involved eccentrically long elf-locks and oiled black curls.}}

(countable) An insufficiency, especially of something essential to health.

* {{quote-magazine, date=2013-08-31, volume=408, issue=8851, magazine=(The Economist)

, title= Promotion and self-promotion , passage=One of academia’s deficiencies is that, though its lecture halls and graduate schools are replete with women, its higher echelons are not. Often, this is seen as a phenomenon specific to the sciences. … In fact, the disparity applies to the whole grove. Another report from 2006, by the American Association of University Professors, found the same ratio in the faculties of arts, humanities and social science, too.}}

(geometry) The amount by which the number of double points on a curve is short of the maximum for curves of the same degree.

(geometry) The codimension of a linear system in the corresponding complete linear system.