Liars gun misfires, only once (8)

I believe the answer is:

singular

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'only once' is the definition.
I can't tell whether this definition defines the answer.

'liars gun misfires' is the wordplay.
'misfires' is an anagram indicator (I've seen 'misfiring' mean this (I've seen this in other clues)).
'liars'+'gun'='liarsgun'
'liarsgun' with letters rearranged gives 'SINGULAR'.

Can you help me to learn more?

(Other definitions for singular that I've seen before include "number" , "distinctive" , "Strange - unique" , "Unusual, maybe unique" , "Odd; unique" .)

I've seen this clue in the Sydney Morning Herald.

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