What W. Slater became (7)

I believe the answer is:

wastrel

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'what w slater became' is the definition.
I can't tell whether this definition defines the answer.

'w slater became' is the wordplay.
'became' indicates anagramming the letters (I've seen 'becomes' mean this).
'slater' anagrammed gives 'astrel'.
'w'+'astrel'='WASTREL'

Can you help me to learn more?

(Other definitions for wastrel that I've seen before include "Worthless person" , "Person who dissipates resources self-indulgently" , "Ne'er-do-well" , "Layabout" , "Good-for-nothing person" .)

I've seen this clue in the Evening Standard.

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