Lack of fairness some strain, I quit yesterday (8)

I believe the answer is:

iniquity

'lack of fairness' is the definition.
(iniquity is wickedness or cruelty)

'some strain i quit yesterday' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'INIQUITY' can be found hidden inside 'strain i quit yesterday'.

(Other definitions for iniquity that I've seen before include "Gross injustice; crime" , "Great wickedness or injustice" , "Heinousness" , "immorality" , "Going wrong" .)

I've seen this clue in The Telegraph.

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