Melancholy G&S? John digs in (10)

I believe the answer is:

gloominess

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'melancholy' is the definition.
(gloominess is a kind of melancholy)

'gs? john digs in' is the wordplay.
'john' becomes 'loo' (loo is a kind of john).
'digs' becomes 'mines' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'loo'+'mines'='loomines'
'gs' placed around 'loomines' is 'GLOOMINESS'.

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(Other definitions for gloominess that I've seen before include "Dimness, obscurity" , "Depression, despondency" .)

I've seen this clue in The Telegraph.

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