Skill or knowledge in a particular field (9)

I believe the answer is:

expertise

'skill or knowledge in a particular field' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for expertise that I've seen before include "Mastery, proficiency" , "Adroitness" , "Special skill or knowledge" , "Thorough knowledge" , "professionalism" .)

I've seen this clue in the Irish Times (Simplex) and The Irish Times.

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