ˈ ̷ ̷ˌ ̷ ̷ noun
1.
a. : a line to which persons may cling to save or protect their lives: as
(1) : one stretched along the deck or from the yards of a ship — see ship illustration
(2) : one attached to a ship or buoy for the use of people in the water
(3) : one stretched through surf for the use of bathers
b. : a line attached to a diver's helmet for use chiefly in raising and lowering him in the water
c. : a rope line by which a person may be lowered to safety (as from a burning building)
2. : something held to resemble a line used for the saving or protection of life
the … program is the very lifeline by which an alcoholic can pull himself back to a normal position in life — Alcoholics Anonymous Grapevine
3. usually capitalized : line of life
4. : a land, sea, or air route regarded as indispensable to life ; especially : one held necessary to supply or communicate with a usually distant outpost or to maintain an empire
severing the Mediterranean lifeline of the empire — Malcolm Wheeler-Nicholson