I confess, supporting Republican revolution (6)
I believe the answer is:
rising
'revolution' is the definition.
(thesaurus)
'i confess supporting republican' is the wordplay.
'confess' becomes 'sing' (I've seen this before).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'republican' becomes 'r' (abbreviation).
'i'+'sing'='ising'
'ising' put after 'r' is 'RISING'.
(Other definitions for rising that I've seen before include "Armed revolt against authority" , "Moving upwards" , "Approaching the age of" , "Ascension" , "Revolt; coming up" .)