As a noun phrase ('a live one'): a lively, spirited, or noteworthy person, event, or specimen; something energetic or strikingly active.
2.
USUKneutral
As a verbal phrase with a numeral unit (e.g., 'live one day'): to continue to live for one additional unit of time; to survive an extra specified measure.
3.
USUKneutral
In contexts meaning 'live one life': to have or lead a single lifetime; used in statements about the limits or choices of an individual's life.