Formal doctor gets a say occasionally (6)
I believe the answer is:
dressy
'formal' is the definition.
(I've seen this in another clue)
'doctor gets a say occasionally' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'gets'+'a'+'say'='getsasay'
The alternate letters of 'getsasay' are 'essy'.
'dr'+'essy'='DRESSY'
(Other definitions for dressy that I've seen before include "Smartly clothed" , "Elaborate" , "Smartly attired, wearing stylish clothes" , "Wearing stylish clothing" , "Nattily attired, wearing stylish clothes" .)