Host inviting in posh clan to participate (4,2)
I believe the answer is:
muck in
'participate' is the definition.
Both the answer and definition are verbs in their base form.
Maybe they are linked in a way I don't understand?
'host inviting in posh clan' is the wordplay.
'host' becomes 'mc' (short for Master of Ceremonies).
'inviting in' means one lot of letters goes inside another.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'clan' becomes 'kin' (synonyms).
'mc' enclosing 'u' is 'muc'.
'muc'+'kin'='MUCK IN'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for muck in that I've seen before include "Lend a hand" , "Help out" , "In slang, share tasks equally - even filthy ones" , "Do one's bit" .)