life·line 
(līflīn′)
(līflīn′)n.
1.
a. An anchored line thrown as a support to someone falling or drowning.
b. A line shot to a ship in distress.
c. A line used to raise and lower deep-sea divers.
2.
a. A means or route by which necessary supplies are transported.
b. One that is or is regarded as a source of salvation in a crisis.
3. A diagonal line crossing the palm of the hand and believed to indicate the length and major events of one's life.