An Aos Si (pronounced EES SHEE) (also known as Sidhe (pronounced as SHEE) meaning "mound" in Irish) is a type of mythological fairy from Irish mythology. It is comparable with fairies and elves. Though they live in underground in fairy mounds across the western sea that coexists with humans, however, it is said their world is described in the Book of Invasions in which a Sidhe can walk amongst the living. Though a Sidhe be stunning and beautiful, it is also described it has a hideous behavior.
There are also other types of Sidhe in Irish mythology:
- Banshee, as an omen of death and messenger of the underworld. Her name is pronounced "Bean Si" (BAN-SHEE).
- Leprechaun, an Irish tiny man who protects its pot of gold near the end of the rainbow.