Lost fear in quarterfinal becoming calm (8)

I believe the answer is:

tranquil

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'calm' is the definition.
(I know that calm can be written as tranquil)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for tranquil that I've seen before include "like Othello's mind before Iago's treachery" , "Peaceful and quiet, not agitated" , "Calm, placid, still" , "Calm and serene" , "Restful" .)

I've seen this clue in The Irish Times.

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