Mattress on ground and many different things (10)

I believe the answer is:

assortment

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'many different things' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'mattress on ground' is the wordplay.
'ground' indicates an anagram ('grind' the letters into a new form).
'mattress'+'on'='mattresson'
'mattresson' with letters rearranged gives 'ASSORTMENT'.

'and' is the link.

Can you help me to learn more?

(Other definitions for assortment that I've seen before include "Medley" , "Miscellany" , "Mixture" , "Variety" , "Miscellaneous collection" .)

I've seen this clue in The Independent.

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