What would be a good classical Latin word for "idiot"? The Latin word idiota seems to refer to an uneducated layman, whereas the English "idiot" means someone of low intelligence. That is, the Latin word refers to low education (uncultivated) but the English one refers to low mental ability (non-cultivable). Perhaps bardus, infacetus, or baro would work, but I am unsure. What would you suggest and why?
Plautus offers a colorful list of synonyms which all roughly translate as "idiot":
Quicúmque ubi ubi sunt, quí fuerunt quiqué futuri sunt pósthac
stultí, stolidi, fatuí, fungi, bardí, blenni, buccónes,
solús ego omnis longe ántideo
stultítia et moribus índoctis. (Pl Bacch 5.1)
Whoever there are in any place whatsoever, whoever have been, and whoever shall be, in time to come, fools, blockheads, idiots, dolts, sots, oafs, lubbers, I singly by far exceed them all in folly and absurd ways.
The footnote explains blennus and bucco:
"Blennus" means, properly, "dirty-nosed," and thence "a driveller," "an idiot." "Bucco" was "one who had large puffed-out cheeks," which was considered to be the mark of a blockhead or foot.
Lewis and Short glosses fungus as an extension of the primary meaning of "mushroom":
A soft-pated fellow, a dolt
And it links bardus to the same root as gravis:
stupid, dull of apprehension
The other words (stultus, stolidus, and fatuus) should be a part of your working insult vocabulary already :)
It seems that stolidus was used for both meanings, the former “uncultivated” and the latter “non-cultivable.” According to Lewis & Short,1
I. Unmovable; and hence, slow, coarse, uncultivated, rude (class.; cf.: fatuus, insipiens, stupidus, stultus, insulsus).—
B. Lit.: stolidum genus Aeacidarum Bellipotentes sunt magi' quam sapientipotentes, Enn. ap. Cic. Div. 2, 56, 116 (Ann. v. 187 Vahl.): “nam vi depugnare sues stolidi soliti sunt,” id. ib. 2, 56, 116 (Ann. v. 109 id.).—
II. Dull, senseless, slow of mind, obtuse, stupid, stolid: “mī stolido,” Plaut. Capt. 3, 4, 123: “stulti, stolidi, fatui, fungi, bardi, blenni, buccones,” Plaut. Bacch. 5, 1, 2: “quid, stolide, clamas?” id. Aul. 3, 2, 1; id. Ep. 3, 3, 40; id. Bacch. 3, 6, 19: “vix tandem sensi stolidus,” Ter. And. 3, 1, 12: indocti stolidique, * Hor. Ep. 2, 1, 184: Lentulus perincertum stolidior an vanior, Sall. ap. Gell. 18, 4, 4 (H. 4, 35 Dietsch): “dux ipse inter stolidissimos,” Liv. 22, 28, 9: “o vatum stolidissime, falleris,” Ov. M. 13, 774.—Of the Stoics, Lucr. 1, 641; 1, 1068.—
Lewis, Charlton T.; Short, Charles. Harper’s Latin Dictionary: A New Latin Dictionary Founded on the Translation of Freund’s Latin-German Lexicon. New York: American Book, 1879.