Old prince more likely to have showers than others? (7)

I believe the answer is:

rainier

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'old prince' is the definition.
(Rainier III of Monaco)

I can't explain the remainder of the clue.

(Other definitions for rainier that I've seen before include "More wet - Monaco's late prince" , "Volcano in Washington" , "Former prince of Monaco" , "weather getting worse" , "more drops?" .)

I've seen this clue in The Sunday Times.

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