Summon Leo, say, for identification (4,4)
I believe the answer is:
call sign
'identification' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?
'summon leo say' is the wordplay.
'summon' becomes 'call' (I've seen this before).
'leo say' becomes 'sign' (leo is a kind of sign).
'call'+'sign'='CALL SIGN'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for call sign that I've seen before include "Identifying code of sender or receiver of broadcast message" , "Unique designation in radio communications" , "A wireless operator's identification" , "Air Force One, say" , "Radio ID" .)