Note short skirt and madam's rear (5)
I believe the answer is:
minim
'note' is the definition.
(minim is a kind of note)
'short skirt and madam's rear' is the wordplay.
'short skirt' becomes 'mini' (I've seen this before**).
'and' is a charade indicator (letters next to each other).
'rear' suggests the final letters (the back of the word).
The final letter of 'madam' is 'm'.
'mini'+'m'='MINIM'
(Other definitions for minim that I've seen before include "Palindromic note" , "Beat" , "Note equal to two crochets" , "Musical note - small amount of liquid" , "Note with value of half a semibreve" .)