Otherwise known as Mrs Alf Garnett
I believe the answer is:
else
'otherwise' is the definition.
(synonyms)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for else that I've seen before include "Besides, otherwise" , "Alternatively" , "Eels (anag)" , "Adverb meaning if not, otherwise" , "Otherwise; different from" .)