Barbarism, n.
Etymology: [L. barbarismus, Gr.; cf. F. barbarisme.]
1. An uncivilized state or condition; rudeness of manners; ignorance of arts, learning, and literature; barbarousness. Prescott.
2. A barbarous, cruel, or brutal action; an outrage. A heinous barbarism . . . against the honor of marriage. Milton.
3. An offense against purity of style or language; any form of speech contrary to the pure idioms of a particular language. See Solecism. The Greeks were the first that branded a foreign term in any of their writers with the odious name of barbarism. G. Campbell.
Shades of meaning
Fernald has no entry of its own for barbarism; 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