Old key needed for lift (5)
I believe the answer is:
exalt
'for lift' is the definition.
(I've seen this before)
'old key needed' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'key' becomes 'alt' (the Alt keyboard button).
'needed' is a charade indicator (letters next to each other).
'ex'+'alt'='EXALT'
(Other definitions for exalt that I've seen before include "Elevate" , "Promote" , "Honour - raise up" , "Uplift in praise" , "Praise highly" .)