Cycloid may refer to:
- Cycloids, a group of one-eyed alien monsters that includes:
- Cycloid Emperor (DN3D), the final boss of Shrapnel City in Duke Nukem 3D
- Cycloid Emperor (DN64), the 3D polygonal boss of Duke Nukem 64
- Cycloid Emperor (DNF), a boss in Duke Nukem Forever
- Cycloid Sentry, a recurring enemy and miniature version of the Cycloid Emperor in Duke Nukem 3D
- Cycloid Incinerator, the final boss of Alien World Order in Duke Nukem 3D: 20th Anniversary World Tour
- Devastator (DN3D), a weapon in Duke Nukem 3D that was originally known as the "Cycloid" in prototypes