Tricky in the extreme? Shorten it drastically (9)

I believe the answer is:

thorniest

I'm a little stuck... Click here to teach me more about this clue!

'tricky in the extreme?' is the definition.
I can't tell whether this definition defines the answer.

'shorten it drastically' is the wordplay.
'drastically' indicates an anagram.
'shorten'+'it'='shortenit'
'shortenit' anagrammed gives 'THORNIEST'.

Can you help me to learn more?

(Other definitions for thorniest that I've seen before include "most problematic" , "Most troublesome or prickly" .)

I've seen this clue in The Guardian.

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