Noah Webster
Idiom
ID'IOM, noun [Latin idioma, from Gr. proper, or peculiar to one's self; Eng. widow, wide.]
1. A mode of expression peculiar to a language; peculiarity of expression or phraseology. In this sense, it is used in the plural to denote forms of speech or phraseology, peculiar to a nation or language.
And to just idioms fix our doubtful speech.
2. The genius or peculiar east of a language.
He followed the Latin language, but did not comply with the idiom of ours.
3. Dialect.