During class, a learner relaxed (8)
I believe the answer is:
informal
'relaxed' is the definition.
(informal can mean relaxed or casual)
'during class a learner' is the wordplay.
'during' becomes 'in' (e.g. during February means in February).
'class' becomes 'form class' (form class is a kind of class).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'in'+'form'+'a'+'l'='INFORMAL'
(Other definitions for informal that I've seen before include "Casual and unceremonious" , "If normal, be casual and without ceremony" , "Unofficial, relaxed" , "Casual or unofficial" , "Casual, not official" .)