Hide mistake by fielder (5,4)

I believe the answer is:

cover slip

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'fielder' is the definition.
Both the definition and answer are singular nouns.
Maybe they are linked in a way I don't understand?

'hide mistake by' is the wordplay.
'hide' becomes 'cover' (covering is a kind of hiding).
'mistake' becomes 'slip' (a slip is a blunder or mistake).
'by' says to put letters next to each other.
'cover'+'slip'='COVER SLIP'

Can you help me to learn more?

(Another definition for cover slip that I've seen is " That comes under the microscope".)

I've seen this clue in The Daily Express.

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