Earl to make clever remark on river for balance (9)
I believe the answer is:
equipoise
'for balance' is the definition.
(synonyms)
'earl to make clever remark on' is the wordplay.
'earl' becomes 'e'.
'to make' becomes 'oise' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'clever remark' becomes 'quip' (a quip is a witty comment).
'on' says to put letters next to each other.
'oise' put after 'quip' is 'quipoise'.
'e'+'quipoise'='EQUIPOISE'
'river' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Another definition for equipoise that I've seen is " balance".)