Some Blairism that's essential in vision (4)
I believe the answer is:
iris
'essential in vision' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'some blairism that's' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'IRIS' is hidden in the letters of 'blairism thats'.
Can you help me to learn more?
(Other definitions for iris that I've seen before include "Bright flower or eye part" , "Ms Murdoch" , "Female" , "Pupil is at the centre of this" , "--- Murdoch, author" .)