Trail minister, one occupying seat (7)

I believe the answer is:

preview

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'trail' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'minister one occupying seat' is the wordplay.
'minister' becomes 'rev' (short for reverend).
'one' becomes 'i' (Roman numeral).
'occupying' is an insertion indicator (inserted letters occupy or enter the word).
'seat' becomes 'pew' (pew is a kind of seat).
'rev'+'i'='revi'
'revi' going within 'pew' is 'PREVIEW'.

Can you help me to learn more?

(Other definitions for preview that I've seen before include "Early chance to see" , "Hint" , "early show" , "A showing before opening night" , "Film trailer" .)

I've seen this clue in The Telegraph.

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