Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
half-life is a noun meaning "the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)". It carries one recorded sense.
the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
Definitions, synonyms and semantic relations for half-life come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.