Crossword Genius

It's said, in annoyance, of many a pest (4)

Ross

I believe the answer is:

drat

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

'it's said in annoyance' is the definition.
I can't tell whether this defines the answer.

'many a pest' is the wordplay.
'many' becomes 'd'.
'a pest' becomes 'rat' (rat can mean a nasty person).
'd'+'rat'='DRAT'

'of' acts as a link.

Can you help me to learn more?

(Other definitions for drat that I've seen before include "Expression of annoyance on DART" , "Minced oath" , "Bother" , "Expression of mild annoyance" , "Curse it!" .)

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