Two of eight, perhaps, heading for unrest in October after revolution (4,4)
I believe the answer is:
cube root
'two of eight perhaps' is the definition.
(two is the cube root of eight)
'heading for unrest in october after revolution' is the wordplay.
'heading for' suggests taking the first letters.
'in' is an insertion indicator.
'after revolution' indicates anagramming the letters.
The first letter of 'unrest' is 'u'.
'october' is an anagram of 'cberoot'.
'u' going inside 'cberoot' is 'CUBE ROOT'.
(Other definitions for cube root that I've seen before include "The 'x' in x3" , "27's is 3" , "4 of 64 or 5 of 125, for example" , "As 7 is of 343" , "3, of 27, for example?" .)