Dance function with Grand Ball (5)
I believe the answer is:
tango
'dance' is the definition.
(tango is a type of dance)
'function with grand ball' is the wordplay.
'function' becomes 'tan' (tangent, mathematical function).
'with' is a charade indicator (letters next to each other).
'grand' becomes 'g' (G is short for grand as in a thousand).
'ball' becomes 'o' (O looks like a ball).
'tan'+'g'+'o'='TANGO'
(Other definitions for tango that I've seen before include "South American dance (for two?)" , "Modern ballroom dance" , "Movement from Argentina" , "One from Argentina" , "Dance of South American origin" .)