Sebastian traces to a Greek honorific meaning "venerable" or "revered," later adapted into Latin as a personal name. Historically it described someone worthy of respect by standing, not necessarily by age, and it has carried a dignified, formal air through centuries of use across several European languages.
Consider what things the Planets perform not by their Aspects, and observe if they do them not by their Antisions, for the Antisions have power, and are not to be enumerated amongst Aspects. - William Lilly (1602.-1681.)