In class a learner initially relaxed (8)
I believe the answer is:
informal
'relaxed' is the definition.
(informal can mean relaxed or casual)
'in class a learner initially' is the wordplay.
'class' becomes 'form class' (synonyms).
'initially' says to take the initial letters.
The first letter of 'learner' is 'l'.
'in'+'form'+'a'+'l'='INFORMAL'
(Other definitions for informal that I've seen before include "Unofficial, relaxed" , "Casual, free and easy" , "Casual or unofficial" , "If normal, be casual and without ceremony" , "Cosy -- loose" .)