No longer is? That’s spurious, firstly! (6)

I believe the answer is:

exists

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'no longer is? that's spurious firstly' is the definition.
I can't tell whether this definition defines the answer.

'no longer is? that's spurious firstly' is the wordplay.
'no longer' becomes 'ex' (prefix meaning former or onetime).
'firstly' indicates taking the first letters.
The initial letters of 'that spurious' is 'ts'.
'ex'+'is'+'ts'='EXISTS'

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(Other definitions for exists that I've seen before include "Has life" , "Lives" , "Has being, is actual" , "Is extant" , "Is present in the universe" .)

I've seen this clue in The Times.

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