A planet was said to be combust when its light was extinguished by proximity to the sun.
Venus and Mercury, when thus 'combust,' lost their influence.
All astrologers agree that a planet is fortified by this position, but a planet when combust is very evil in its influences.
When Venus and Mercury were ‘combust’ their influence was lost.
late 14c. as an adjective, "burnt," from Old French combust (14c.), from Latin combustus, past participle of combuere "to burn up, consume" (see combustion). Also an astrological term for planets when near the sun. The verb is attested from late 15c. Related: Combusted; combusting.