Quick answer
Rhiannon is a girl name meaning "great queen".
Pronunciation: Welsh /r̥ɪ.ˈan.ɔn/; English /ɹi.ˈæn.ən/.
Meaning and history
Probably derived from an unattested Celtic name * Rīgantonā meaning "great queen" (Celtic * rīganī "queen" and the divine or augmentative suffix -on ). It is speculated that Rigantona was an old Celtic goddess, perhaps associated with fertility and horses like the Gaulish Epona. As Rhiannon, she appears in Welsh legend in the Mabinogi as a beautiful magical woman who rides a white horse. She was betrothed against her will to Gwawl, but cunningly broke off that engagement and married Pwyll instead. Their son was Pryderi. As an English name, it became popular due to the Fleetwood Mac song Rhiannon (1976), especially in the United Kingdom and Australia.
Notes and context
Usage: welsh, english, welsh mythology