From WordNet (r) 3.0 (2006) [wn]:
lettered
adj 1: highly educated; having extensive information or
understanding; "knowing instructors"; "a knowledgeable
critic"; "a knowledgeable audience" [syn: knowing,
knowledgeable, learned, lettered, well-educated,
well-read]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Letter \Let"ter\ (l[e^]t"t[~e]r), v. t. [imp. & p. p. Lettered
(-t[~e]rd); p. pr. & vb. n. Lettering.]
To impress with letters; to mark with letters or words; as, a
book gilt and lettered.
[1913 Webster] letter bomb
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Lettered \Let"tered\ (l[e^]t"t[~e]rd), a.
1. Literate; educated; versed in literature. " Are you not
lettered?" --Shak.
[1913 Webster]
The unlettered barbarians willingly accepted the aid
of the lettered clergy, still chiefly of Roman
birth, to reduce to writing the institutes of their
forefathers. --Milman.
[1913 Webster]
2. Of or pertaining to learning or literature; learned. " A
lettered education." --Collier.
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3. Inscribed or stamped with letters. --Addison.
[1913 Webster]