Casts off Dublin girlfriends having unusual sides (6)
I believe the answer is:
moults
'casts off' is the definition.
(moulting is a kind of casting off)
'dublin girlfriends having unusual sides' is the wordplay.
'dublin girlfriends' becomes 'mots' (I can't explain this - if you can you should believe this answer much more).
'having' means one lot of letters goes inside another.
'sides' says to hollow out the word (remove centre letters) (only the letters on the sides are used).
'unusual' with its middle removed is 'ul'.
'mots' placed around 'ul' is 'MOULTS'.
Can you help me to learn more?
(Other definitions for moults that I've seen before include "Shed hair or skin prior to new growth" , "Sheds feathers or skin" , "Sheds fur or feathers" .)