| X class submarine | Classe X |
| X Division | X Division |
| X Factor | X-Factor |
| X Japan | X Japan |
| X Prize Foundation | X Prize Foundation |
| X ray | Raggi X |
| X ray absorption | Assorbimento di raggi X |
| X ray astronomy | Astronomia X |
| X ray background | Fondo X |
| X ray bright point | Punti brillanti X |
| X ray burst | Burst X |
| X ray diffraction | Diffrazione di raggi X |
| X ray flare | Brillamenti X |
| X ray fluorescence | Fluorescenza da raggi X |
| X ray identification | Identificazioni di sorgenti X |
| X ray line | Righe X |
| X ray nova | Stelle novae X |
| X ray observatory | Osservatori X |
| X ray polarization | Polarizzazione X |
| X ray pulsar | Pulsar X |
| X ray quasar | Quasar X |
| X ray radiation | Radiazione X |
| X ray scattering | Diffusione X |
| X ray source | Sorgenti X |
| X ray spectrographs | Spettrografi X |
| X ray spectroscopy | Spettroscopia X |
| X ray spectrum | Spettri X |
| X ray structure | Struttura X |
| X ray survey | Survey X |
| X ray transients | Transienti X |
| X rays | Raggi X |
| X window manager | Window manager |
| X-bar theory | Teoria x-barra |
| X-chromosome | cromosoma X |
| X-Factor | X-Factor |
| X-inactivation | Effetto Lyon |
| X-mas | Natale |
| X-Men | X-Men |
| X-radiation | Raggi X |
| X-ray | lastra |
| X-ray absorption spectroscopy | Spettroscopia XAS |
| X-ray crystallography | Diffrazione dei raggi X |
| X-ray diffraction | Diffrazione dei raggi X |
| X-ray fluorescence | Spettrofotometria XRF |
| X-ray photo | Radio |
| X-ray photoelectron spectroscopy | Spettroscopia fotoelettronica a raggi X |
| X-ray photography | Radio |
| X-ray picture | lastra |
| X-ray spectroscopy | Spettrofotometria XRF |
| X-rays | raggi X |
| X-wing | X-wing |
| Xabi Alonso | Xabi Alonso |
| Xagħra | Caccia |
| Xai-Xai | Xai-Xai |
| Xaignabouli | Xaignabouli |
| Xaignabouli Province | Xaignabouli |
| Xaisomboun | Xaisomboun |
| Xanadu | Xanadu |
| Xanadu House | Xanadu |
| Xanana Gusmão | Xanana Gusmão |
| Xanatos | Xanatos |
| Xander Harris | Xander Harris |
| XANES | XANES |
