| Wellentheorie | wave model wave theory |
| Zelltheorie | cell theory |
| Zahlentheorie | theory of numbers |
| Mengentheorie | set theory |
| Knotentheorie | knot theory |
| Dramentheorie | dramatic theory |
| Wellenform | waveform |
| wellenförmig | undulate wave-shaped wavy |
| Graphentheorie | graph theory |
| Gruppentheorie | group theory |
| Quantentheorie | quantum theory |
| Eichtheorie | gauge theory |
| Spieltheorie | game theory |
| Systemtheorie | system theory |
| Wellenbrecher | breakwater |
| Wellenleiter | waveguide |
| Wellenreiher | Malayan night heron |
| Wellenreiten | surfing |
| wellenreiten | surf |
| Wellenreiter | surfer |