Crossword Genius

Should find nothing missing, initially (5)

Ross

I believe the answer is:

ought

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'should' is the definition.
(synonyms)

I cannot understand how the remainder of the clue works.

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(Other definitions for ought that I've seen before include "Tough (anag)" , "It expresses duty or obligation" , "Should, had, better" , "Verb implying duty; zero, nothing (archaic)" , "Anything at all (archaic)" .)

I've seen this clue in The Daily Express.
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