Helping a learner is sensible (8)
I believe the answer is:
rational
'sensible' is the definition.
(associated in meaning)
'helping a learner' is the wordplay.
'helping' becomes 'ration' (a ration is a serving or helping).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'ration'+'a'+'l'='RATIONAL'
'is' is the link.
(Other definitions for rational that I've seen before include "Not absurd" , "Logical; sensible" , "Based on reason or logic" , "Logical, reasoned" , "Sane; able to think" .)