Dependent on setting one tax cut, unexpectedly large (10)

I believe the answer is:

contextual

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'dependent on' is the definition.
Although both the answer and definition are adjectives, I can't understand how they can define each other.

'one tax cut unexpectedly large' is the wordplay.
'unexpectedly' indicates an anagram.
'large' becomes 'L' (eg in clothes sizes).
'one'+'tax'+'cut'='onetaxcut'
'onetaxcut' with letters rearranged gives 'contextua'.
'contextua'+'l'='CONTEXTUAL'

'setting' is the link.

Can you help me to learn more?

(Another definition for contextual that I've seen is " Relating to surrounding words".)

I've seen this clue in The Telegraph.

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