Landing sea power (4)

I believe the answer is:

main

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This could be a double definition.

'landing sea' is the first definition.
'main' can be an answer for 'sea' (synonyms). I am unsure of the 'landing' bit.

'power' is the second definition.
(thesaurus)

Can you help me to learn more?

(Other definitions for main that I've seen before include "Source of water" , "Cardinal" , "location for 9 [ARMADA]" , "Chief - principal electricity cable" , "Chief in importance" .)

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

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