* "twelf": Meaning "twelve"
* "mōnaþ": Meaning "month"
Therefore, "twelvemonth" literally translates to "twelve months," which is a year. The term likely emerged as a way to refer to a year in a more specific and literal way than simply "year," emphasizing the number of months that constitute it.
The use of "twelvemonth" became common in Old English and Middle English, and it remained in use throughout the 16th and 17th centuries. However, its usage declined over time, and today it is considered somewhat archaic or poetic, though still understood.
The term "twelvemonth" is a good example of how idioms can be formed by combining existing words in a way that creates a new meaning. It also reflects how language can evolve over time, with older terms being replaced by newer ones as usage shifts.