More wet in volcano (7)
I believe the answer is:
rainier
This clue is a double definition.
'more wet' is the first definition.
('rainy' can be similar in meaning to 'wet')
'volcano' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for rainier that I've seen before include "Former prince of Monaco" , "More wet - Monaco's late prince" , "more drops?" , "This is more likely to pour down" , "Prince of Monaco, married to Grace Kelly, d. 2005" .)