"Irreantum, which being interpreted, is, many waters." . . . Proof of this, Mr. Nephi Mormon Moroni Rigdon Harris Cowdery Smith. Let us have the proof. Irreantum signifies a complete ass, nearer than anything else.
Origen Bacheler, Mormonism Exposed Internally and Externally (1838), 14
Nephi says "We beheld the sea, which we called Irreantum, which being interpreted, is many waters" (1 Nephi 17:5). Nephi's wording suggests that this may not have been a name from his native language. Years ago Hugh Nibley suggested a possible Egyptian derivation for the name (Since Cumorah, 1988, 171-72), but his proposal has not persuaded other Latter-day Saint linguists. More recently John Gee, Paul Hoskisson and Brian Hauglid have argued, that the name does make sense as a South Semitic name meaning "watering of completeness" or "watering of (super)abundance" which is consistent with Nephi's interpretation of the name.
For a more complete discussion, see the Book of Mormon Onomasticon entry.