Sister's pal picked up unbridled sarcasm (6)
I believe the answer is:
matron
'sister's' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for matron that I've seen before include "One used to be in charge of hospital nurses" , "Medical supervisor" , "Former title of today's Senior Nursing Officer" , "Woman in charge of nurses" , "Senior nursing officer of old" .)