- infertile
- infirm
- infirmities of agedness
- inflammable
- inflection
- inflict
- influx
- inform
- infraction
- infrequent
- ingratiating
- inhabit
- inhumane
- inimical
- initiate
- injurious
- inkling
- inland
- inmate
- inmost
- inner impurity
- innocent
- inoculate
- inoffensive
- inoperative
- inquest
- inquisition
- inquisitor
- inscribe
- insinuation
- inspector
- inspiring
- instability
- institute
- institution
- instrument
- insubordination
- insubstantial
- insular
- insulting
- insurgent
- intemperance
- inter
- intercept
- interdict
- interject
- interjection
- intermediate
- intermission
- internal-combustion engine
- interpolate
- interrogate
- intestines
- intolerable
- intolerant
- intranet
- intrepid
- intriguing
- invariable
- invective
- invest
- invigorate
- invincible
- invisible
- invitation
- invite
- invocation
- invoke
- involve
- invulnerable
- ionisation enthalpy
- ire
- Ireland
- irregular
- irrelevance
- irreparable
- irrepressible
- irresistible
- irresistibly
- irrespective
- irritability
- irritably
- irritate
- isochrony
- isolate
- it is snowing
- itemize
- iterate
- itinerary
- in the balance
- in decline
- infectious
- in the doldrums
- in doubt
- in high dudgeon
- in any event, at all events
- in evidence
- in fact
- in favour of
- in fits and starts, by fits and starts