Fats Waller wrote about these (10)

I believe the answer is:

waterfalls

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'these' is the definition.
The definition suggests an adverb but the answer is not.

'fats waller wrote about' is the wordplay.
'wrote about' indicates an anagram (I've seen 'written about' mean this (letters moved about before being rewritten)).
'fats'+'waller'='fatswaller'
'fatswaller' is an anagram of 'WATERFALLS'.

Can you help me to learn more?

(Other definitions for waterfalls that I've seen before include "Up north, forces" , "Cataracts" .)

I've seen this clue in The Irish Independent.

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