King upset over old woman's abnormal dryness (6)

I believe the answer is:

xeroma

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'dryness' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'king upset over old woman's abnormal' is the wordplay.
'king' becomes 'rex' ('king' in Latin).
'upset over' says the letters should be written backwards (knocked over).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'woman's abnormal' becomes 'ma' (I can't explain this - if you can you should give a lot more credence to this answer).
'rex' written backwards gives 'xer'.
'xer'+'o'+'ma'='XEROMA'

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I've seen this clue in The Independent.

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