Silas likely derives from the Latin silva, forest, arriving by way of Greek use as a companion form to Silvanus. The association with woodland gives the name an untamed, natural undertone -- something rooted outdoors rather than shaped by more formal or urban origins.
Immobility of a slow celestial body is more efficient than the dynamism of a quick one, even though they have the same strength. - Picatrix (Andalusia, ~1000.AD)