Brilliant star not initially espousing strict diet (5)

I believe the answer is:

vegan

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'espousing strict diet' is the definition.
I know that 'diet' relates to this answer.

'brilliant star not initially' is the wordplay.
'brilliant star' becomes 'vega' (star in the constellation Lyra. I am not sure about the 'brilliant' bit.).
'initially' says to take the initial letters.
The initial letter of 'not' is 'n'.
'vega'+'n'='VEGAN'

Can you help me to learn more?

(Other definitions for vegan that I've seen before include "An extreme vegetarian" , "Avoiding animal products" , "Selective consumer" , "Person refraining from eating animal products" , "Person refraining from using animal products in any way" .)

I've seen this clue in The Irish Times.

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