Kabbalah Yesaya 54:6: Sha'arei Kedusha

It is likewise written,⁴²⁰Proverbs 10:22 – The root Etzev-עצב of this verse is explained to mean “suffering” or “burdensome toil” (see Rashi), however, the simple meaning of the root Etzev-עצב is “sadness” or “melancholy,” as in the verse (Isaiah 54:6), “For like a wife who is forlorn and melancholy (Atzoovah-עצובה), HaShem-יהו״ה has called you. Can one cast off the wife of his Youth? Said your God.” (See Radak to Isaiah 54:6 ibid.) “The blessing of HaShem-יהו״ה is what enriches, and sadness (Etzev-עצב) does not increase it.” For, sadness is drawn from the contamination of Sama’el⁴²¹  This is the angelic name of Satan-the Accuser. and the snake, who infected Adam and Chavah with it, as it states about Adam,⁴²²Genesis 3:17 “With sadness (Eetzavon-עצבון) you shall eat of it all the days of your life,” and about Chava it states,⁴²³Genesis 3:16 “I will greatly increase your sadness (Eetzavon-עצבון)… with sadness (b’Etzev-בעצב) you shall bear children.”⁴²⁴As explained in the prior note, the root Etzev-עצב can mean “suffering” or “sadness.” In context to the subject being explained here, it means “sadness.”