Crossword Genius

Big job for cigar and soup-mix! (6,4)

Ross

I believe the answer is:

magnum opus

I'm a little stuck... Click here to teach me more about this clue!

'big job' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?

'cigar and soup-mix' is the wordplay.
'cigar' becomes 'magnum' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' says to put letters next to each other.
'mix' is an anagram indicator.
'soup' is an anagram of 'opus'.
'magnum'+'opus'='MAGNUM OPUS'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for magnum opus that I've seen before include "Writer's greatest work" , "Great work" , "one's best" , "finest creation" , "Greatest work of an artist" .)

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