A learner having little vitality gets permit (5)
I believe the answer is:
allow
'permit' is the definition.
(I know that permit can be written as allow)
'a learner having little vitality' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'having little vitality' becomes 'low' (in low spirits).
'a'+'l'+'low'='ALLOW'
'gets' is the link.
(Other definitions for allow that I've seen before include "brook" , "Permit or acknowledge" , "Permit or concede" , "Permit or agree" , "Permit, consent to" .)