Siobhán is a common Irish Gaelic female given name. It is pronounced shiv-awn (IPA /ʃɪˈvɔːn/), and so may sometimes be spelled Shevaun and Shivaun.
It is derived from the Hebrew name Yôḥānān (יוֹחָנָן) which means "God is gracious", which has over time given us John, Jane, Sean, and Joan, among many, many others. The Anglo-Norman forms Jehane and Jehanne arrived in Ireland in the late 1100s, and was adopted into local languages as something akin to Sibán.
There are a large number of variations on the name. The diminutive form is Siobháinín, in Gaelic; however it is more common to see Sinéad (shin-ayd, IPA /ʃɪˈneɪd/), a Gaelic form of the French diminutive Jeannette. In Scottish Gaelic the name is spelled Siubhan; oddly, this is often translated as Judith, which does not have a tie to the actual root of the name. The male Irish form of the name is Sean (which morphed into Eathain or Iain in Scottish Gaelic). It appears that Sean was used as a base for a new female name, Séadna or Séanna, which we usually see today spelled as Shauna.