Some rabbis mocked specific doctrine (3)
I believe the answer is:
ism
'specific doctrine' is the definition.
(I've seen this before)
'some rabbis mocked' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ISM' can be found hidden inside 'rabbis mocked'.
(Other definitions for ism that I've seen before include "Any ideological doctrine" , "Ideological movement" , "form of belief?" , "Informal noun or suffix for doctrine or practice" , "Distinctive theory" .)