Celebrate noisily (7)
'celebrate noisily' is the definition.
(roistering is a kind of celebrating noisily)
This is the entire clue.
(Other definitions for roister that I've seen before include "Be boisterous" , "Revel noisily, swagger" , "I rest or (anag) - engage in noisy merrymaking" , "Celebrate noisily" , "Carouse" .)
'celebrate noisily' is the definition.
(synonyms)
This is all the clue.