Being plump, bachelor wears Ben’s suit badly (9)

I believe the answer is:

tubbiness

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'being plump' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

'bachelor wears ben's suit badly' is the wordplay.
'bachelor' becomes 'B' (abbreviation e.g. BA=Bachelor of Arts).
'wears' indicates putting letters inside.
'badly' indicates anagramming the letters (letters in the wrong order).
'bens'+'suit'='benssuit'
'benssuit' is an anagram of 'tubiness'.
'b' put inside 'tubiness' is 'TUBBINESS'.

Can you help me to learn more?

(Another definition for tubbiness that I've seen is " needing to slim down from this state?".)

I've seen this clue in The Times.

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