お団子

Etymology 1
Compound of.

Noun

 * 1)  a traditional Japanese sweet round dumpling

Etymology 2
By analogy from the shape of a single dango, much as the term is used in English to refer to a food item and a hairstyle of a similar shape.

Noun

 * 1) a bun hairstyle

Usage notes
The hairstyle is never referred to as dango without the o- prefix.