Eccentric Christmas visitor sits for attendant (9)
I believe the answer is:
assistant
'for attendant' is the definition.
(thesaurus)
'eccentric christmas visitor sits' is the wordplay.
I cannot really see how this works, but
an anagram of 'sits' is 'sist' which is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for assistant that I've seen before include "Deputy, subordinate" , "second" , "Aide, helper" , "One helping" , "help required?" .)