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.
When a Planet who is a Fortune is in Conjunction with an Infortune, he allays his malice, so that the Infortune shall do no hurt. - William Lilly (1602.-1681.)