Webster's Revised Unabridged Dictionary · 1913

I

I (ī)

1.
I, the ninth letter of the English alphabet, takes its form from the Phonician, through the Latin and the Greek. The Phonician letter was probably of Egyptian origin. Its original value was nearly the same as that of the Italian I, or long e as in mete. Etymologically I is most closely related to e, y, j, g; as in dint, dent, beverage, L. bibere; E. kin, Anglo-Saxon cynn; E. thin, Anglo-Saxon þynne; E. dominion, donjon, dungeon.

The dot which we place over the small or lower case i dates only from the 14th century. The sounds of I and J were originally represented by the same character, and even after the introduction of the form J into English dictionaries, words containing these letters were, till a comparatively recent time, classed together.

2.
In our old authors, I was often used for ay (or aye), yes, which is pronounced nearly like it.
3.
As a numeral, I stands for 1, II for 2, etc.

I- , prefix

See Y-.

I (ī) , pronoun

[Old English i, ich, ic, Anglo-Saxon ic; akin to Old Saxon & Dutch ik, Old High German ih, German ich, Icelandic ek, Danish jeg, Swedish jag, Gothic ik, OSlav. az', Russ. ia, Welsh i, Latin ego, Greek 'egw`, 'egw`n, Sanskrit aham. r179. Compare Egoism.]

The nominative case of the pronoun of the first person; the word with which a speaker or writer denotes himself.