| I. | Island; one (Roman). |
| i. | Intransitive. |
| ib., ibid. | Ibidem (Latin), in the same place. |
| I.C. | Indo-China; internal combustion. |
| i/c. | In charge of. |
| I.C.I. | Imperial Chemical Industries. |
| LC.S. | Indian Civil Service; International Correspondence Schools. |
| id. | Idem (Latin), the same. |
| Ida. | Idaho. |
| I.D.B. | Illicit diamond buyer. |
| I.D.C. | Imperial Defence College. |
| I.E. | Indo-European. |
| i.e. | Id est (Latin), that is. |
| I.G. | Industrien Gesellschaft (a German chemical combine); Inspector General. |
| I.H.S. | Jesus Hominum Salvator (Latin), Jesus, the Saviour of mankind. |
| Ill. | Illinois. |
| illus. | Illustrated by; illustration(-s). |
| I.L.O. | International Labour Office. |
| i.l.o. | In lieu of. |
| I.L.P. | Independent Labour Party. |
| Imp. | Imperator (Latin), emperor; imperial. |
| imp. | Imperative; imperfect (grammar); import(-s)(-ed); impression (publishing); imprimatur (Latin), let it be printed. |
| in. | Inch. |
| Inc. | Incorporated. |
| incl | Including; inclusive. |
| incog. | Incognito (Italian), unknown. |
| Ind. | Independent; index; Indian; Indiana; industrial. |
| I.N.D. | In nomine Dei (Latin), in God's name. |
| ind. | Indicative. |
| inf. | Infinitive; information; infra (Latin), below, or further on. |
| infra dig. | Infra dignitatem (Latin), beneath dignity. |
| I.N.I. | In nomine Jesus (Latin), in the name of Jesus. |
| in loc. | In loco (Latin), in its place. |
| inns. | Innings. |
| in pr. | In principio (Latin), in. the first place. |
| I.N.R.I. | Jesus Nazarenus Rex Judaeorum. (Latin), Jesus of Nazareth, King of the Jews. |
| Ins. | Inspector; insurance. |
| I.N.S. | International News Service. |
| Insc. | Inscribed. |
| Insp. | Inspector. |
| inst. | Instants mense (Latin), in the present month; institute(-d). |
| int. | Interest; interim; interior; internal; interval. |
| int. al. | Inter alia (Latin), among other things. |
| Inter. | Intermediate examination. |
| intr. | Intransitive. |
| Intro. | Introduction. |
| introd. | Introduced. |
| inv. | Invented; invoice(-d) |
| lo. | Iowa. |
| I.O. | India Office; Intelligence officer. |
| I.O.M. | Isle of Man. |
| I.O.W. | Isle of Wight. |
| I.P.A. | India pale ale. |
| I.Q. | Intelligence quotient. |
| i.q. | idem quod (Latin), the same as. |
| I.R. | Inland Revenue. |
| I.R.A. | Irish Republican Army. |
| I.R.C. | International Red Cross. |
| I.R.O. | Inland Revenue Office. |
| Is. | Book of Isaiah; islands. |
| It. | Italian (usually of vermouth). |
| Ital. | Italian; italic. |
| I.W. | Isle of Wight. |
| I.W.T. | Inland water transport. |
| I.W.W. | Industrial Workers of the World. |
| I.X. | Jesus Christ. |