The name Thelonius is a boy's name of Latin origin meaning "lord". Thelonius and is often added to lists like Attitude Names for Boys and discussed in our forums with posts like "Spelling Bee Name Game".
From the experts:
One of the coolest of names, thanks to legendary jazz pianist Thelonious Sphere Monk, who inherited it from his father. It has been used very sparingly since the 1960s--just a sprinkling of baby boys receive the name each year. Monk's middle name Sphere is pretty unique too--a cousin of Cosmos and Cosmo. Some other jazz names to consider: Bix, Ellington, Ella, Etta, Mingus, Dexter and Calloway. :