Mathematics & Geometry:
* Dodecagon: A polygon with twelve sides.
* Dodecahedron: A polyhedron with twelve faces.
Other:
* Dodecasyllable: A word or phrase consisting of twelve syllables.
* Dodecaphonic: Relating to a musical system using a twelve-tone scale.
These are just a few examples, and there might be other less common words using the prefix "dodeca-".