Isolated a section (5)
I believe the answer is:
apart
'isolated' is the definition.
(I know that isolated can be written as apart)
'a section' is the wordplay.
'section' becomes 'part' (synonyms).
'a'+'part'='APART'
(Other definitions for apart that I've seen before include "aloof" , "in isolation" , "Separated; to one side" , "Separated physically" , "First Christmas present from my love" .)