Imbolc means 'in the belly', im - within, bolc - belly, but has many variant names. Another possible source for the name is from the Irish 'imb fholc', washing oneself. This could result from the purification aspects of the holiday.

The Irish called it Óimelc (Middle Irish) or Ouimelko (Old Irish), meaning 'ewe's milk' (oi - sheep, melc - milk). Other spellings for the holiday include Imbolg, Oimelk and Oímelg. In Scots Gaelic, the holiday is called Là Féill Bhride (holiday of Brid or Brigit). Another Irish name for the holiday is Lá 'il Bríde (day of Brid or Brigit). In common modern Irish and Manx, the holiday is called Candlemas Day.

-Taken from The Wheel of the Year at Muin Mound Grove, ADF by  Rev. Skip Ellison