Writer takes exam without company at Whitsuntide (9)

I believe the answer is:

pentecost

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'whitsuntide' is the definition.
(I've seen this before)

'writer takes exam without company' is the wordplay.
'writer takes' becomes 'pen' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'exam' becomes 'test' (synonyms).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'company' becomes 'co' (abbreviation).
'test' placed around 'co' is 'tecost'.
'pen'+'tecost'='PENTECOST'

'at' is the link.

Can you help me to learn more?

(Other definitions for pentecost that I've seen before include "Whitsuntide" , "Christian festival on Whit Sunday" .)

I've seen this clue in The Globe and Mail.

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