half-life

the compound noun 'half-life' is a modern scientific formation built from two ancient english roots. 'half' originates from the old english 'healf', which carried the sense of a side or portion, a meaning preserved in its modern use to denote one of two equal parts. 'life' derives from old english 'līf', referring to the state of existence or the duration of that state. the term was coined in the early 20th century within physics and chemistry, combining these common words to create a precise technical concept: the period required for a quantity to reduce to half its initial value, metaphorically applying the idea of a "lifetime" measured in halves rather than a complete cycle.

Structure: half (one of two equal parts) + life (duration of existence) half: from old english 'healf', meaning "side, part", and from proto-germanic halbaz, meaning "divided". functions as a quantifier meaning "one of two equal parts". life: from old english 'līf', meaning "existence, lifetime", and from proto-germanic libam. functions as a noun denoting a duration or period of existence.