Crossword Genius

Rubber, ruler, neither right (3)

Ross

I believe the answer is:

ule

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'neither right' is the definition.
The definition suggests a singular noun which matches the answer.

'rubber ruler' is the wordplay.
'ULE' is hidden within the letters.
However, I'm uncertain how this is indicated.

Can you help me to learn more?

(Another definition for ule that I've seen is " Rubber tree".)

I've seen this clue in The Independent.
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