Murmur about a strange blemish or rash (5-6)
I believe the answer is:
harum-scarum
'rash' is the definition.
(I've seen this before)
'murmur about a strange blemish' is the wordplay.
I cannot quite understand how this works, but
'about' could be 'ca' (abbreviation for 'circa') and 'ca' is present in the answer.
'a' is within the answer.
'strange' could be 'rum' (similar in meaning) and 'rum' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'or' is the link.
(Other definitions for harum-scarum that I've seen before include "Reckless, impetuous" , "Rash" , "Wild and thoughtless" , "Cheerfully irresponsible" , "Wild and reckless" .)