double Dutch

Etymology

double (twice, i.e. more than) + Dutch For sense 1: The English, historically, found Dutch (albeit a fellow Western Germanic language) particularly difficult to understand, so anything that was completely incomprehensible would be double Dutch, i.e. twice as hard as Dutch. (Note that historically, "Dutch" could refer to German dialects, as well.)

Noun

double Dutch (uncountable)

1. Incomprehensible language.
2. A language game akin to pig Latin.
3. A game of jump rope with two ropes and frequently two jumpers.
4. (colloquial) Sex using a condom and the contraceptive pill at the same time.