Definition - An error in grammar, diction, or speech.

Example -
Whom ate my pizza?

Etymology -
The word derives via French and Latin from the Greek soloikismos, to speak incorrectly.
Note: The latter derives from soloikos, which in Greek means "a speaking like the people of Soloi." Soloi was an Athenian colony in Cilicia, and the Athenians considered the Soloian dialect barbarous. In Vancouver we use the term calgarism, a speaking like the people of Calgary.

Oxford English Dictionary -
Its first citation is from 1577:
"They seeme farre from offending, in any barbarous terme, solœcisme, or ignorant error at all."
( Hanmer Anc. Eccl. Hist. (1585), 138)

Quotation -
"The grammarians used to distinguish between barbarism, incorrectness in the use of words, and solecism, incorrectness in the construction of sentences."
(Source: Fowler's Modern English Usage s.v. solecism )

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