Watery sound is so spacious (6)

I believe the answer is:

rheumy

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'watery' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

(Other definitions for rheumy that I've seen before include "damp and unhealthy" , "Of eyes, having moist discharge" , "Of eyes or nose, having watery discharge" , "Catarrh-filled" , "congestion" .)

I've seen this clue in The Irish Times.

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