Left omen about something sharp (5)

I believe the answer is:

lemon

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'something sharp' is the definition.
I can't tell whether this defines the answer.

'left omen about' is the wordplay.
'left' becomes 'L' (common abbreviation).
'about' is an anagram indicator.
'omen' with letters rearranged gives 'emon'.
'l'+'emon'='LEMON'

Can you help me to learn more?

(Other definitions for lemon that I've seen before include "Useless object" , "A fruit; a worthless item" , "very different from peach?" , "Strong yellow colour" , "Fruit-tree" .)

I've seen this clue in The Mirror.

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