Be slow to grasp new question without agitation (8)
I believe the answer is:
tranquil
'without agitation' is the definition.
'be slow to grasp new question' is the wordplay.
'be slow' becomes 'trail'.
'to grasp' is an insertion indicator.
'new' becomes 'n'.
'question' becomes 'qu'.
'n'+'qu'='nqu'
'trail' placed around 'nqu' is 'TRANQUIL'.
(Other definitions for tranquil that I've seen before include "composed" , "Peaceful - calm" , "Unruffled" , "Serenely quiet or peaceful" , "Peaceful and serene" .)