>"-us" is not a sure sign of a masculine gender in nouns. All those -us nouns of the fourth declension are neutral. And it's not masquerading as masculine, it is neutral and proudly and regularly so. It's just regular by a rule you weren't aware of :).

NEUTER! Neutral is a driving non-gear, or lack of opinion, or stance, etc. :-)

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>Other than that, you got it right :).
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>>OK, the rest follows without the explanation. Thanks. Still think it should be "opus magnum" though :-)
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>It is.

I hear them say "Magnum Opus" on British high-brow programs

- Whoever said that women are the weaker sex never tried to wrest the bedclothes off one in the middle of the night
- Worry is the interest you pay, in advance, for a loan that you may never need to take out.