(countable, offensive) Someone who has immigrated into a country by bypassing customs and immigration controls.

(mathematics) A mathematical problem, asking whether a room with mirrored walls can always be illuminated by a single-point light source, allowing for repeated reflection of light off the mirrored walls. It was solved in 1958: there are such rooms that cannot be thus illuminated.

An optical illusion in which parallel lines are made to appear convergent or divergent by means of oblique intersections.

Abbreviation of illustration.

plural of illegal immigration

The optical illusion resulting from the Thatcher effect.

(psychology) The psychological illusion by which people tend to believe that their personalities and preferences have reached a more or less stable state, despite recognising that these things have undergone significant change in the past.

plural of illegal forward kick

plural of illegal number

plural of illegal combatant