fellatio

The story

1. Proto-Indo-European*dʰeh₁(y)-
2. Latinfellō
3. Latinfellātiō
4. English todayfellatio

Learned borrowing from Latin fellātiō, from fellātus, perfect participle of fellō (“to suck, to fellate”). The word started to appear in medical literature in the 19th century but it was still treated as Latin. In 1919, the California Supreme Court struck down a law criminalizing fellatio because the state constitution required laws to be written in English. By the late 20th century, fellatio was treated as an English word.