The cloth covered button on the crown is about the size of a bean seed and may be the origin of the term "beanie". Some academics believe that the term is instead derived from a type of headgear worn in some medieval universities.
The urban dictionary, the source of many a defination to broaden your vocabulary defines said garment as .... "a beanie is usually woollen and it is worn by skaters and people who are cold"
Fredercik: I’m Freezing!!
Angelina: Of course you are, you forgot your beanie!