Celebrates founder of communism, we hear (5)
I believe the answer is:
marks
'celebrates' is the definition.
(marking is a kind of celebrating)
'founder of communism we hear' is the wordplay.
'founder of communism' becomes 'marx' (I've seen this before).
'we hear' shows a homophone (sound like).
'marx' sounds like 'MARKS'.
(Other definitions for marks that I've seen before include "Former German currency" , "Grades assigned to school work" , "Targets" , "Visible signs" , "Stains" .)