WWI battle – attempt to secure old position – horrific affair (11)

I believe the answer is:

monstrosity

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'horrific affair' is the definition.
The answer and definition can be both related to natural events as well as being singular nouns.
Maybe you can see a link between them that I can't see?

'wwi battle attempt to secure old position' is the wordplay.
'wwi battle' becomes 'mons' (I can't explain this - if you can you should believe this answer much more).
'attempt' becomes 'try' (I've seen this before).
'to secure' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'position' becomes 'sit' (sitting is a kind of positioning).
'o'+'sit'='osit'
'try' placed around 'osit' is 'trosity'.
'mons'+'trosity'='MONSTROSITY'

Can you help me to learn more?

(Other definitions for monstrosity that I've seen before include "Grossly ugly object" , "ugly skyscraper?" , "Something hideous" .)

I've seen this clue in The Independent.

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