What is the origin of the names of the months of the year?

The first 6 months are named for various dieties and legendary figures, though there are disputes as to exactly how a few of the names were created. Janus --> January is clear; Mars --> March is also clear. The last four months of the year have odd origins. September, the 9th month, comes from the Latin for seventh; October from Latin for 8th and November and December for 9th and 10th. These Words come from a very old Latin calendar with only 10 months; months were added into the calendar for Caesar Julius and Caesar Augustus. These months pushed back the last four months and made the names rather foolish. (There is an alternate explanation provided by some sources January and February were actually the inserted months; in that explanation July was "fifth" and August "sixth"). February comes from a combination of old English and Latin roots for month of purification. The name of April is disputed and may come from a ceremony honoring Venus. May and June also have some dispute.