Subject settled with unknown currency (10)
I believe the answer is:
topicality
'currency' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?
'subject settled with unknown' is the wordplay.
'subject' becomes 'topic' (synonyms).
'settled' becomes 'alit' (I've seen this before).
'with' says to put letters next to each other.
'unknown' becomes 'y' (algebra).
'topic'+'alit'+'y'='TOPICALITY'
Can you help me to learn more?
(Another definition for topicality that I've seen is " Editor likes to have this".)