Dialect, n.
Etymology: [F. dialecte, L. dialectus, fr. Gr. Dialogue.]
1. Means or mode of expressing thoughts; language; tongue; form of speech. This book is writ in such a dialect As may the minds of listless men affect. Bunyan. The universal dialect of the world. South.
2. The form of speech of a limited region or people, as distinguished from ether forms nearly related to it; a variety or subdivision of a language; speech characterized by local peculiarities or specific circumstances; as, the Ionic and Attic were dialects of Greece; the Yorkshire dialect; the dialect of the learned. In the midst of this Babel of dialects there suddenly appeared a standard English language. Earle. [Charles V.] could address his subjects from every quarter in their native dialect. Prescott.
Syn. -- Language; idiom; tongue; speech; phraseology. See Language, and Idiom.
Shades of meaning
Fernald has no entry of its own for dialect; he lists it under language.
Where he writes about it:
A dialect is a special mode of speaking a language peculiar to some locality or class, not recognized as in accordance with the best usage; a barbarism is a perversion of a language by ignorant foreigners, or some usage akin to that. — from language
A dialect may be used by the highest as well as the lowest within its range; a patois is distinctly illiterate, belonging to the lower classes; those who speak a patois understand the cultured form of their own language, but speak only the degraded form, as in the case of the Italian lazzaroni or the former negro slaves in the United States. — from language