A tough direction (6)

I believe the answer is:

astern

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'direction' is the definition.
The answer and definition are not the same part of speech.

'a tough' is the wordplay.
'tough' becomes 'stern' (both can mean strict or severe).
'a'+'stern'='ASTERN'

Can you help me to learn more?

(Other definitions for astern that I've seen before include "Behind (a boat)" , "Towards the rear of a ship" , "(In relation to ship) behind" , "Behind (naut.)" , "Ran set (anag.)" .)

I've seen this clue in the Evening Standard.

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