Crossword Genius

The earth's five main features (6)

Ross

I believe the answer is:

oceans

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'the earth's five main features' is the definition.
I can't judge whether this defines the answer.

'main features' is the wordplay.
'main' becomes 'ocean' (synonyms).
'features' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'ocean'+'s'='OCEANS'

Can you help me to learn more?

(Other definitions for oceans that I've seen before include "Great seas" , "Atlantic, Pacific etc" , "Arctic and Indian" , "Large bodies of water" , "Vast bodies of water" .)

I've seen this clue in The Guardian, The Globe and Mail and The Telegraph.
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