- Io
- io moth
- iodic acid
- iodide
- iodin
- iodinate
- iodinated
- iodinated protein
- iodinating
- iodination
- iodine
- iodine-125
- iodine-131
- iodise
- iodised
- iodize
- iodized
- iodoamino acid
- iodochlorhydroxyquin
- iodocompound
- iodoform
- iodoprotein
- iodopsin
- iodothyronine
- iodotyrosine
- IOL
- ion
- ion beam
- ion engine
- ion exchange
- ion pump
- ionate
- Ionesco
- Ionia
- Ionian
- Ionian order
- Ionian Sea
- Ionic
- ionic beam
- ionic bond
- ionic charge
- Ionic dialect
- ionic medication
- Ionic order
- ionisation
- ionise
- ionised
- ionization
- ionization chamber
- ionization tube
- ionize
- ionized
- ionizing radiation
- ionophoresis
- ionosphere
- ionospheric wave
- iontophoresis
- iontotherapy
- IOP
- Iosif Vissarionovich Dzhugashvili
- iota
- IOU
- Iowa
- Iowa crab
- Iowa crab apple
- Iowan
- Ioway