Such twins were once inseparable (7)
I believe the answer is:
'such' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for siamese that I've seen before include "like a cat" , "sort of twins" , "Pale breed of cat" , "Cat with slanting blue eyes and pale fur with darker points" , "cats?" .)