What’s in water regularly dissolves (4)
I believe the answer is:
isle
'what's in water' is the definition.
I can't judge whether this defines the answer.
'regularly dissolves' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'dissolves' are 'ISLE'.
Can you help me to learn more?
(Other definitions for isle that I've seen before include "The Lake ... of Innisfree (W.B.Yeats)" , "Lilliput, say" , "Small bit of land surrounded by water" , "Eg, Sheppey" , "This could be key" .)