Being dirty, one falls into serious condition (9)

I believe the answer is:

griminess

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'being dirty one falls into serious condition' is the definition.
I can't tell whether this defines the answer.

'one falls into serious condition' is the wordplay.
'one' becomes 'i' (Roman numeral).
'falls into' indicates putting letters inside.
'serious' becomes 'grim'.
'condition' becomes 'ness' (I can't justify this - if you can you should believe this answer much more).
'grim'+'ness'='grimness'
'i' put into 'grimness' is 'GRIMINESS'.

Can you help me to learn more?

(Other definitions for griminess that I've seen before include "Quality of coal" , "Amount of muck" .)

I've seen this clue in The Times.

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