Encourage revolutionary queen (5)
I believe the answer is:
'encourage' is the definition.
(cheering is a kind of encouraging)
'revolutionary queen' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
(Other definitions for cheer that I've seen before include "Inspirit" , "Root" , "Vocal sound of applause" , "Applaud vocally, hurray etc" , "Merriment" .)