My first instinct upon seeing this name was that it was "made up." In my defense, it does look like a compound of Belle and Millicent. But looks can be deceiving. Bellicent's (pronounced "BEL-ih-sent" I think) meaning is unknown, but it is possibly related to Belenus, the Celtic god of the sun. If this is true, it would therefore mean "brilliant" or "bright." Some sources list Bellicent as a boy's name. I'm not sure I'm buying it, but I might as well mention it.
Bellicent is a character in Arthurian legend. If you haven't heard of her before, that's probably because she sometimes goes by another name, Morgause. Bellicent is the half-sister of King Arthur and the mother of Gareth and Gawain. She is mentioned in the epic poem "The Idyll of Gareth and Lynette" by Alfred Lord Tennyson.
In the poem, Gareth longs to become a knight of the round table, but Bellicent doesn't want him to go as he is her last son. She orders him to go to Camelot to serve as an anonymous kitchen servant for a year and a day, thinking that he wouldn't obey. To her disappointment, he does as he is told. After Gareth serves King Arthur well for the time his mother says, Bellicent has no choice but to allow him to become a Knight.
This name is almost unknown in the United States. There are a handful of Bellicents that I could find, and all of them are older. But the timing seems right for Bellicent. With Isabelle on top, Belle names are in vogue. And of course, this names sounds very similar to Bellatrix, without the villainous connotations.
Bellicent certainly has a nice witchy sound that's very dignified. And Witches generally do love Arthurian legend. At the moment, Bellicent is the only girls name beginning with the letter B that I would consider for my own daughter as a first name. I wonder when others will share my love and place it in the top 1,000, although mostly I wish that it will stay unique.