Crossword Genius

An old truth about Mike's flat (6)

Ross

I believe the answer is:

smooth

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'flat' is the definition.
(thesaurus)

'an old truth about mike's' is the wordplay.
'an old truth' becomes 'sooth' (synonyms. I am not sure about the 'old' bit.).
'about' means one lot of letters goes inside another.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'sooth' enclosing 'm' is 'SMOOTH'.

Can you help me to learn more?

(Other definitions for smooth that I've seen before include "Hairless" , "Easy" , "Regular - without problems" , "Even-surfaced" , "Free from roughness or irregularities" .)

I've seen this clue in The Guardian.
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