Dashiell's exact origin is uncertain, generally traced to a French surname possibly meaning "page boy" or attendant, though the connection is looser than for many older names. It's become associated instead with a spirited, adventurous character, largely through its use by a well-known 20th-century writer.
You can address Mercury on the empty signs while the Moon can be addressed on both positions indistinctively. - Picatrix (Andalusia, ~1000.AD)