Have a quiet word with Mike, say (6)
I believe the answer is:
mutter
'have a quiet word' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'with mike say' is the wordplay.
'with' means one lot of letters go next to another.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'say' becomes 'utter' (to utter something is to speak or say it).
'm' put next to 'utter' is 'MUTTER'.
Can you help me to learn more?
(Other definitions for mutter that I've seen before include "Low continuous sound" , "Speak indistinctly or grumble" , "Barely audible utterance" , "Speak or grumble in low clear voice" , "Talk under one's breath" .)