After function, leave for dance (5)
I believe the answer is:
tango
'for dance' is the definition.
(Tango is a dance)
'after function leave' is the wordplay.
'after' is a charade indicator (letters next to each other).
'function' becomes 'tan' (tangent, mathematical function).
'leave' becomes 'go' (to go is to depart or leave).
'tan'+'go' is 'TANGO'.
(Other definitions for tango that I've seen before include "Last - in Paris (film)" , "uniform to follow" , "something seen in ballroom?" , "tee" , "Dramatic dance form Argentina" .)