Prospecting for oil is tedious (6)

I believe the answer is:

boring

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'tedious' is the definition.
(I know that tedious can be written as boring)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for boring that I've seen before include "Mentally wearying" , "Tedious and tiring" , "flat" , "Making holes" , "Tedious, tiresome" .)

I've seen this clue in The Irish News.

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