Trim men when dancing welcoming outsiders from earlier jollity (9)
I believe the answer is:
merriment
'jollity' is the definition.
(I've seen this before)
'trim men when dancing welcoming outsiders from earlier' is the wordplay.
'when dancing' is an anagram indicator (letters dance around).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'outsiders from' says to hollow out the word (remove centre letters) (letters on the outside of the word).
'earlier' with its middle taken out is 'er'.
'trim'+'men'='trimmen'
'trimmen' is an anagram of 'mriment'.
'mriment' going around 'er' is 'MERRIMENT'.
(Other definitions for merriment that I've seen before include "laughing maybe" , "Joy" , "Hilarity" , "Gaiety, laughter, fun" , "Jollity" .)