Singer caught in irregular maelstrom (4)

I believe the answer is:

alto

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'singer' is the definition.
(type of singing voice)

I cannot understand how the rest of the clue works.

(Other definitions for alto that I've seen before include "One who sings" , "Singing range" , "The highest adult male singing voice" , "Highest male voice: lowest female voice" , "Voice part" .)

I've seen this clue in The Irish Times.

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