Relative: 'M' for it in audible accent? (3)
I believe the answer is:
sis
'relative' is the definition.
(short for sister)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sis that I've seen before include "relative" , "Secret Intelligence Service (abbr.)" , "Sibling (informal)" , "Family member (informal)" , "Girl" .)