Neither thanks mass uprising for CO (6)
I believe the answer is:
matron
'co' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'neither thanks mass uprising' is the wordplay.
'neither' becomes 'nor' (eg in the phrase 'neither do I').
'thanks' becomes 'ta' (UK informal version of 'thank you').
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'uprising' says the letters should be written in reverse.
'nor'+'ta'+'m'='nortam'
'nortam' reversed gives 'MATRON'.
'for' is the link.
(Other definitions for matron that I've seen before include "Woman in charge of nurses" , "Senior nursing officer of old" , "Chief nurse" , "school officer" , "Middle-aged or elderly married woman" .)