Seas's inlets eroding main points (10)
I believe the answer is:
essentials
'seas's inlets' is the definition.
The answer and definition can be both natural objects as well as being plural nouns.
Perhaps there's a link between them I don't understand?
'eroding main points' is the wordplay.
I cannot really see how this works, but
'points' could be 'ess' (east and south are compass points) and 'ess' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for essentials that I've seen before include "Things needed" , "necessities" .)