
zeitlebens
throughout life
During one's whole life; from birth until death.
Sie hat zeitlebens in diesem kleinen Dorf gewohnt.
She lived in this small village throughout her life.
throughout one's life
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throughout life
During one's whole life; from birth until death.
Sie hat zeitlebens in diesem kleinen Dorf gewohnt.
She lived in this small village throughout her life.
'Zeitlebens' (throughout one's life) is made up of the words 'Zeit' (time) and 'Leben' (life). It is a shortened form of the old genitive expression '(seiner) Zeit des Lebens', meaning 'during the time of one's life'.
Er blieb seiner Heimat zeitlebens treu.
He remained loyal to his homeland throughout his life.
As an adverb, 'zeitlebens' (throughout one's life) can stand in position 1; then the verb follows in position 2. It can also stand after the conjugated verb in the middle of the sentence.
Zeitlebens hat er hart für seine Familie gearbeitet.
Throughout his life, he worked hard for his family.
This adverb belongs more to written language or an elevated style. It is used less often in normal everyday conversation.
Die Künstlerin hat zeitlebens für ihre Anerkennung gekämpft.
The artist fought for recognition throughout her life.
lifelong / life
Both words describe a duration covering a person's entire life. Lebenslang usually appears as an adjective with a noun and can also be used adverbially. Zeitlebens is only an adverb and often looks back on an entire life that has already been lived; this determines which form is used in practice.

Er pflegte zeitlebens eine enge Freundschaft mit seinem Nachbarn.
Throughout his life, he maintained a close friendship with his neighbor.
Er hatte eine lebenslange Freundschaft mit seinem Nachbarn.
He had a lifelong friendship with his neighbor.