(astronomy) A unit of length (abbreviation ly; equal to just under 10 trillion kilometres (10¹⁶ metres)) equal to the distance light travels in one Julian year; used to measure extremely large distances.

(chemistry) Water in its standard form of H₂O, containing two protium hydrogen atoms, as opposed to heavy water.

The amount of light falling on a given area, as measured by units such as the lumen.

(physics) The speed of electromagnetic radiation; in a perfect vacuum it is defined as 299,792,458 metres per second / (colloquial, figuratively) A very rapid speed.

(intransitive, cricket, of the umpires) To ask the batsmen if they wish to continue playing in conditions of poor light. If they do not, play is suspended for bad light.

(cricket) A weather condition where the light is so poor that the umpires feel that to continue playing would be dangerous. / (figuratively) An unfavourable presentation.

(uncountable) Light in the ultraviolet part of the spectrum. / (countable) A light bulb that emits ultraviolet light; a black light.

(countable) A light bulb that emits ultraviolet light, usually used to create the illusion that anything white is glowing. / (uncountable, slang) ultraviolet radiation/light

A source of illumination.

Ground combat soldiers who are not mechanized, and whose role is to harass the enemy in front of the main body of infantry.