Plaintiff to express annoyance at worker (11)

I believe the answer is:

complainant

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'plaintiff' is the definition.
(synonyms)

'annoyance at worker' is the wordplay.
'annoyance at' becomes 'complain' (I am not sure about this - if you are sure you should believe this answer much more).
'worker' becomes 'ant' (worker is a type of ant).
'complain'+'ant'='COMPLAINANT'

'to express' is the link.

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(Another definition for complainant that I've seen is " One bringing an action".)

I've seen this clue in The Irish Times.

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