Celebrate former superior officer (5)
I believe the answer is:
exult
'celebrate' is the definition.
(I've seen this before)
'former superior officer' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'superior' becomes 'U' (U can mean upper-class, as in U and non-U speech).
'officer' becomes 'lt' (abbreviation for lieutenant).
'ex'+'u'+'lt'='EXULT'
(Other definitions for exult that I've seen before include "Rejoice exceedingly, glory in (5)" , "Be intensely joyful" , "Express great joy" , "Gloat" , "Be jubilant" .)