Essential oil filling rings is never drunk (4)
I believe the answer is:
otto
'essential oil' is the definition.
(I've seen this before)
'filling rings is never drunk' is the wordplay.
'filling' means one lot of letters goes inside another.
'rings' becomes 'oo' (multiple circles).
'is never drunk' becomes 'TT' (short for teetotal).
'oo' going around 'tt' is 'OTTO'.
(Other definitions for otto that I've seen before include "Swiss perhaps" , "____ Preminger, US film director born in Austria" , "Emperor's" , "Essential oil from flowers - German boy's name" , "Reversible German" .)