Everything opened essentially, using this type of key? (5)

I believe the answer is:

allen

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'this type of key?' is the definition.
The definition suggests a singular noun which matches the answer.

'everything opened essentially' is the wordplay.
'everything' becomes 'all' (all things).
'essentially' indicates the central letters.
The middle of 'opened' is 'en'.
'all'+'en'='ALLEN'

'using' acts as a link.

Can you help me to learn more?

(Other definitions for allen that I've seen before include "Woody ..., US film maker" , "Woody ... is film director and comic actor" .)

I've seen this clue in The Irish Times.

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