What's in the sea? Unopened maps from the East (4)
I believe the answer is:
salt
'what's in the sea?' is the definition.
I can't tell whether this defines the answer.
'unopened maps from the east' is the wordplay.
'unopened' means to remove the first letter (without opening letter).
'maps' becomes 'atlas' (printed collection of maps).
'from the east' says the letters should be written backwards (on a map from right to left).
'atlas' with its initial letter taken away is 'tlas'.
'tlas' backwards is 'SALT'.
Can you help me to learn more?
(Other definitions for salt that I've seen before include "A defence against ice" , "Preserve" , "Condiment - old sailor" , "Mariner; sodium chloride" , "Wit; sodium chloride" .)