Lightweight knocked out on cue (5)

I believe the answer is:

ounce

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'lightweight' is the definition.
(light unit of weight)

'out on cue' is the wordplay.
'out' indicates an anagram.
'on'+'cue'='oncue'
'oncue' with letters rearranged gives 'OUNCE'.

'knocked' acts as a link.
This may not be correct. It may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for ounce that I've seen before include "weight? Surely not" , "One cat" , "Lightweight" , "One sixteenth of a pound" , "Unit equal to about 28 grams" .)

I've seen this clue in The Telegraph.

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