So wrong in the case of that which is plural! (5)
I believe the answer is:
those
'case of that which is plural' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'so wrong in the' is the wordplay.
'wrong' indicates an anagram.
'in' is an insertion indicator.
'so' with letters rearranged gives 'os'.
'os' put inside 'the' is 'THOSE'.
Can you help me to learn more?
(Other definitions for those that I've seen before include "the more far out?" , "Plural form of that" , "Nostalgic utterance" , "The (things) there" , "The ones farther away" .)