One maxi coat of obvious style (9)
I believe the answer is:
axiomatic
'one' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'maxi coat of obvious style' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is found in the answer.
an anagram of 'maxi' is 'axim' which is present in the remaining letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for axiomatic that I've seen before include "Self-evidently true" , "Accepted" , "Given" , "Pertaining to self-evident truths" , "Taken for granted" .)