- irish bull
- ineptitude
- inner vision
- innermost
- incase
- ingrowing
- ingrid bergman
- imitation
- irredentism
- ismaili
- islets of langerhans
- inductee
- investigator
- intermezzo
- interlude
- irrational motive
- imaginary creature
- imaginary being
- intoxication
- inevitable accident
- isoptin
- inorganic phosphate
- infinitesimal calculus
- incalescence
- Islamic calendar month
- infatuation
- intestinal bypass
- in a class by itself
- in a class by oneself
- in a class of own
- in a class of its own
- immerse
- inebriate
- invade
- in use
- ilo
- ilx
- Iliamna
- Isatis
- Irena
- Iridoprocne
- Indicatoridae
- Irenidae
- impala lily
- Ilex cornuta
- indigo plant
- Irish gorse
- Indigofera tinctoria
- Indian currant
- Indian rhododendron