Crossword Genius

Having slap-up meal but missing first course (7)

Ross

I believe the answer is:

easting

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'course' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

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(Other definitions for easting that I've seen before include "distance in another direction" , "distance for navigator" , "Map reference" , "oriental course?" , "distance measured" .)

I've seen this clue in The Telegraph.
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