Emily Dickinson Lexicon

JAN'U-A-RY, n. [Ir. gionbhar or gionvar; Russ. genvar; Fr. janvier; It. gennaio; Sp. enero; Port. janeiro; L. januarius. It is evident from the Irish and Russian words, that the first syllable of January, is from the root of L. geno to beget, Eng. to begin, Sax. aginnan. Var is said to signify a revolution. January then signifies the beginning, or first month. Janus is probably from the same root.]

The first month of the year, according to the present computation. At the foundation of Rome, March was considered the first month. January and February were introduced by Numa Pompilius. – Encyc.