Reportedly squander sentence on vital statistic (9)

I believe the answer is:

waistline

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'vital statistic' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'reportedly squander sentence' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'squander' becomes 'waste' (synonyms).
'sentence' becomes 'line' (I can't explain this - if you can you should give a lot more credence to this answer).
'waste' sounds like 'waist'.
'waist'+'line'='WAISTLINE'

'on' is the link.

Can you help me to learn more?

(Other definitions for waistline that I've seen before include "Swine tail (anag.)" , "Girth" , "It goes round trunk" , "measurement" .)

I've seen this clue in The Daily Express.

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