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 "Boys Drop 2 Add 1 pick a favor that can't be dropped".
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. :