Rough quotation of energy nonsensical at times (8)

I believe the answer is:

estimate

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'rough quotation' is the definition.
'estimate' can be an answer for 'quotation' (I've seen this before). I'm not sure about the 'rough' bit.

'energy nonsensical at times' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'nonsensical' indicates an anagram.
'at'+'times'='attimes'
'attimes' is an anagram of 'stimate'.
'e'+'stimate'='ESTIMATE'

'of' is the link.

Can you help me to learn more?

(Other definitions for estimate that I've seen before include "Form opinion of - tea times (anag)" , "Likely amount" , "Statement giving the likely cost of a job" , "rough judgment" , "Guess, rough calculation" .)

I've seen this clue in The Telegraph.

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