Ptolemy's Essential Dignities and Debilities
Essential dignity, in the context of an astrological horoscope or natal chart, refers to the relative “strength” or “weakness” of a planet based on its zodiac sign and specific degree.
This strength or weakness is referred to as the planet’s essence—what the 17th-century astrologer William Lilly called "the strength, fortitude or debility of the Planets [or] significators."[1]