50 in split to form extremist group (4)
I believe the answer is:
cult
'form extremist group' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'50 in split' is the wordplay.
'50' becomes 'l' (Roman numeral).
'in' is an insertion indicator.
'split' becomes 'cut' (synonyms).
'l' going within 'cut' is 'CULT'.
'to' is the link.
Can you help me to learn more?
(Other definitions for cult that I've seen before include "Group with system of formal worship" , "unorthodox organisation" , "Esoteric religion" , "Unorthodox or false religion" , "System of religious beliefs and rituals" .)