Eat with marine left in back (7)

I believe the answer is:

support

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'back' is the definition.
(synonyms)

'eat with marine left' is the wordplay.
'eat' becomes 'sup' (supping is a kind of eating).
'with' means one lot of letters go next to another.
'marine left' becomes 'port' (left side of a ship - opposite of starboard. I am not sure about the 'marine' bit.).
'sup'+'port'='SUPPORT'

'in' is the link.

Can you help me to learn more?

(Other definitions for support that I've seen before include "comfort" , "Uphold" , "Give assistance to" , "Maintain, back" , "Buttress" .)

I've seen this clue in the Sydney Morning Herald.

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