The Collaborative International Dictionary of English v.0.48:

Illiterate \Il*lit"er*ate\, a. [L. illiteratus: pref. il- not +
   literatus learned. See In- not, and Literal.]
   Unable to read or write; ignorant of letters or books;
   unlettered; uninstructed; uneducated; as, an illiterate man,
   or people.

   Syn: Ignorant; untaught; unlearned; unlettered; unscholary.
        See Ignorant. -- Il*lit"er*ate*ly, adv. --
        Il*lit"er*ate*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

illiterate
    adj 1: not able to read or write [ant: literate]
    2: uneducated in the fundamentals of a given art or branch of
       learning; lacking knowledge of a specific field; "she is
       ignorant of quantum mechanics"; "he is musically illiterate"
       [syn: ignorant, illiterate]
    3: lacking culture, especially in language and literature [ant:
       literate]
    n 1: a person unable to read [syn: illiterate, illiterate
         person, nonreader]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "illiterate":
   Gothic, Philistine, barbarous, benighted, bookless, dabbler,
   deceived, dilettante, dunce, empty-headed, fool,
   functionally illiterate, grammarless, greenhorn, greeny, heathen,
   hoodwinked, ignoramus, ignorant, ill-educated, illiterati,
   know-nothing, led astray, lowbrow, middlebrow, misinformed,
   misinstructed, mistaught, no scholar, nonintellectual, pagan,
   puddinghead, rude, tenderfoot, unbooked, unbookish, unbooklearned,
   unbriefed, uncultivated, uncultured, unedified, uneducated,
   unenlightened, unerudite, unguided, uninstructed, unintellectual,
   unintelligentsia, unlearned, unlettered, unliterary, unread,
   unrefined, unscholarly, unschooled, unstudious, untaught,
   untutored



Bouvier's Law Dictionary, Revised 6th Ed (1856):

ILLITERATE. This term is applied to one unacquainted with letters.
     2. When an ignorant man, unable to read, signs a deed or agreement, or
makes his mark instead of a signature, and he alleges, and can provide that
it was falsely read to him, he is not bound by it, in consequence of the
fraud. And the same effect would result, if the deed or agreement were
falsely read to a blind man, who could have read before he lost his sight,
or to a foreigner who did not understand the language. For a plea of "laymen
and unlettered," see Bauer v. Roth, 4 Rawle, Rep. 85 and pp. 94, 95.
     3. To induce an illiterate man, by false representations and false
reading, to sign a note for a greater amount than that agreed on, is
indictable as a cheat. 1 Yerg. 76. Vide, generally, 2 Nels. Ab. 946; 2 Co.
3; 11 Co. 28; Moor, 148.