The Dutch word for cap is
pet

Dutch Definition

pet	©
1. n-m. cap (headwear with a peak at the front)
2. adj. (slang) bad, crappy

dop
1. n-m. A shell (of an egg or a fruit for example).
Beter een half ei dan een hele dop. - Better half an egg than a whole (empty) shell.
2. n-m. A hemispherical container such as a thimble.
3. n-m. A bottle cap.
4. n-m. (chiefly in the plural) An eyelid.
Kijk uit je doppen! - Look out!
5. n-m. (Belgium) The dole, unemployment benefit.
6. v. first-person singular present indicative of doppen
7. v. imperative of doppen