Before you settle for mono, say (6)
I believe the answer is:
prefix
'mono say' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'before you settle' is the wordplay.
'before' becomes 'pre'.
'you settle' becomes 'fix' (I can't justify this - if you can you should give a lot more credence to this answer).
'pre'+'fix'='PREFIX'
'for' is the link.
Can you help me to learn more?
(Other definitions for prefix that I've seen before include "'Pre-', for example" , "Word placed before another to change its meaning" , "What goes on before" , "Something added to the start of a word - title before a name" , "Un- or re-, say" .)