- X ray
- xylem
- X-ray diffraction
- X-ray film
- X-ray machine
- xenon
- xylophone
- X
- x-axis
- X-linked
- X-radiation
- x-ray
- X-raying
- X-SCID
- Xanax
- xanthate
- xanthelasma
- xanthemia
- xanthine
- Xanthium
- xanthoma
- xanthomatosis
- xanthomonad
- Xanthomonas
- Xanthophyceae
- xanthophyl
- xanthophyll
- xanthopsia
- Xanthorrhoeaceae
- Xanthorroea
- xanthosis
- Xanthosoma
- xanthous
- Xantusiidae
- Xavier
- XC
- xci
- xcii
- xciii
- xciv
- xcl
- xcv
- xcvi
- xcvii
- xcviii
- Xe
- Xenarthra
- Xenicidae
- Xenicus
- xenogenesis
- xenograft
- xenolith
- Xenophanes
- xenophobia
- xenophobic
- Xenophon
- Xenopodidae
- Xenopus
- Xenorhyncus
- Xenosauridae
- Xenosaurus
- xenotime