Unusual case taken by loyal advisor (10)
I believe the answer is:
consultant
'advisor' is the definition.
(synonyms)
'unusual case taken by loyal' is the wordplay.
'case' means to remove the middle letters.
'taken by' means one lot of letters goes inside another.
'loyal' becomes 'constant'.
'unusual' with its centre removed is 'ul'.
'ul' going into 'constant' is 'CONSULTANT'.
(Other definitions for consultant that I've seen before include "See 1 across" , "Senior hospital doctor" , "Specialist" , "Adviser" .)