Festivity involves five in a lively dance (5)
I believe the answer is:
revel
'festivity' is the definition.
(I know that revel is a type of festivity)
'five in a lively dance' is the wordplay.
'five' becomes 'V' (Roman numeral).
'in' means one lot of letters goes inside another.
'a lively dance' becomes 'reel' (I've seen this in another clue).
'v' inserted within 'reel' is 'REVEL'.
'involves' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for revel that I've seen before include "Be festive, enjoy" , "Riotous feast" , "Be festive, have a good time" , "Have a few drinks etc." , "Make merry; luxuriate (in)" .)