Solemn quality a drunkard lacks? (9)

I believe the answer is:

soberness

'quality a drunkard lacks?' is the definition.
(a drunk is not sober)

'solemn' is the wordplay.
I cannot really understand how this works, but
'solemn' could be 'sober' (synonyms) and 'sober' is found in the answer.
The remaining letters 'ness' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

(Another definition for soberness that I've seen is " Gravity".)

I've seen this clue in The Times.

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