(physics) The time required for half the nuclei in a sample of a specific isotope to undergo radioactive decay.

Life outside of a contrived or fantastical environment; often used in comparison to events depicted in drama. / (by extension, sometimes capitalized) Life outside the Internet.

An individual's interpersonal relationships with people within their immediate surroundings or general public. / Those public activities performed in association with others for the purpose of pleasure.

Alternative form of life buoy

Alternative spelling of lifestyle

(idiomatic) An occupation, role, social class, or lifestyle.

That is the way things happen / Certain things cannot be changed, helped or improved; struggle and objection are pointless.

Alternative spelling of lifespan.

(of a person) The amount of time one is expected to live. / (figuratively, by extension, of an idea or an object) The amount of time something is expected to last.

(idiomatic, UK) Mouth-to-mouth resuscitation.