Sage comes directly from the Latin sapere, to know, shared by both the English word for wisdom and the herb long associated with clear-headed judgment. The name states its meaning plainly -- discernment named outright rather than implied through symbol or story.
Mercury being strong and in proper places of the Heavens, well configurated of other stars or planets in nativities, denotes convenient dignity to the native thereby; but Mercury of himself is a planet weak. - William Lilly (1602.-1681.)