Woman's number, having changed sides (5)
I believe the answer is:
ethel
'woman's' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
(Other definitions for ethel that I've seen before include "- Merman, US musical comedy star" , "- Merman, US actress" , "girl" , "Female name" , "- Barrymore, actress" .)