Signal after air-raid, say, everyone understood (3-5)
I believe the answer is:
all clear
'signal after air-raid say' is the definition.
'all clear' can be an answer for 'signal' (I've seen this before). I'm not sure about the 'after air-raid say' bit.
'everyone understood' is the wordplay.
'everyone' becomes 'all' (all people).
'understood' becomes 'clear' (is that clear?).
'all'+'clear'='ALL-CLEAR'
Can you help me to learn more?
(Other definitions for all clear that I've seen before include "welcome sound" , "Siren sound to signal end of air raid" , "old signal to get out of bunker?" , "cue for renewed action" , "unlike 21 [GREY AREAS] ?" .)