With trouble mounting, is willing to participate in casual affair (7)
I believe the answer is:
liaison
'affair' is the definition.
(synonyms)
'with trouble mounting is willing' is the wordplay.
'with' is a charade indicator (letters next to each other).
'trouble' becomes 'ail' (synonyms).
'mounting' is a reversal indicator (in a down clue, letters mount or go up).
'willing' becomes 'on' (I've seen this in other clues).
'ail' written backwards gives 'lia'.
'lia' put next to 'is' is 'liais'.
'liais'+'on'='LIAISON'
'to participate in casual' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for liaison that I've seen before include "Naughty affair?" , "Communication between people or organisations" , "Bond of union" , "Communication; relationship" , "Communication between groups or units" .)