Template:Random Latin fact/nobiscum
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The Roman statesman Cicero had a folk etymological explanation for why we say nobiscum and not cum nobis.
Why don't we say cum nōbīs, but rather nōbīscum? Because: If we say it the other way, the letters would run together in a rather obscene way.—Marcus Tullius Cicerō, Orātor ad Brūtum, § 154
The joke is: cum nōbīs can easily be misunderstood as cunnō bīs which has a lewd meaning, that we are not going to explain here.