Singer caught in maelstrom occasionally (4)
I believe the answer is:
alto
'singer' is the definition.
(type of singing voice)
'maelstrom occasionally' is the wordplay.
'occasionally' indicates alternate letters.
The alternating letters of 'maelstrom' are 'ALTO'.
'caught in' is the link.
(Other definitions for alto that I've seen before include "Voice part" , "someone to sing" , "Singer's hidden inside chemical toilet" , "Low female singing voice" , "Unisex vocal range" .)