Other ranks generally disheartened by revelry (4)
I believe the answer is:
orgy
'revelry' is the definition.
(orgy is a kind of revelry)
'other ranks generally disheartened by' is the wordplay.
'other ranks' becomes 'or' (military abbreviation).
'disheartened' says to hollow out the word (remove centre letters).
'by' says to put letters next to each other.
'generally' with its centre taken out is 'gy'.
'or'+'gy'='ORGY'
(Other definitions for orgy that I've seen before include "Overindulgent revel" , "Excessive indulgence" , "debauched scene" , "Frenzy; bacchanalia" , "Depraved scene" .)