Desperate religious festival with cross upside-down (2-2-3)
I believe the answer is:
do-or-die
'desperate' is the definition.
('do or die' can describe a desperate situation)
'religious festival with cross upside-down' is the wordplay.
'religious festival' becomes 'eid' (I've seen this before).
'with' says to put letters next to each other.
'cross' becomes 'rood' (term for a crucifix).
'upside down' says the letters should be written in reverse.
'eid'+'rood'='eidrood'
'eidrood' in reverse letter order is 'DO-OR-DIE'.
(Other definitions for do-or-die that I've seen before include "'Theirs not to reason why, theirs but to . . . . . . .' (2.2,3)" , "Make an attempt regardless of cost" , "Showing a determination not to compromise" , "Make a desperate effort whatever the consequences" , "Involving a final desperate attempt" .)