What is meant by He is Shaul the son of the Canaanite … He is Zimri? Vilna Gaon to Deut. 29:17
Dvarim/Deut. 29:17 Perhaps there is among you a man, woman, family, or tribe, whose heart strays this day from Hashem, your L-rd, and who goes and worships the gods of those nations; perhaps there is among you a root whose fruit is gall and wormwood”.
The Vilna Gaon in his Aderet Eliyahu commentary explains: “The root from which will sprout from it bad frutis. Gall and Wormwood – Just as our sages of blessed memory stated, ‘the idol of Micha passed over with Israel in the sea’. Now behold there were several centuries between the two events. But rather it is the root from which sprouted the man, Micha that served the idol. That is what passed over with them and it is similar to the departure of the Divine Presence from Yaakov/Jacob when he saw Ephraim, that would sprout from him Yarovom ben Nevat/Jeroboam the son of Nevat; and so too did they say in the Talmud, tractate Sanhedrin 82b, He is Zimri the son of Salu, he is Shelumiel son of Tzuri-shaddai he is Shaul the son of the Canaanite. Now heaven forbid that Zimri has the same soul as the righteous Shelumiel, the choice one of Israel; but rather it is in the manner of ‘it is a disgrace for him, a disgrace for his family and his tribe’. Now the sin sprouted from the root, from Shaul the son of the Canaanite. And this is the root whose fruit is gall and wormwood”.
(Septuagint; xole in Greek). Rosh in Hebrew; see Deuteronomy, 32:32, Jeremiah 9:14, Hosea 10:4, Psalms 69:22, Lamentations 3:19. Or, ‘poison,’ or ‘venom’ (Saadia; Radak, Sherashim; Bachya); cf. Deuteronomy, 32:33, Amos 6:12. Some sources identify rosh with hemlock (Conium maculatum), a dark poisonous plant. Others identify it with gall poppy (Papaver somniferum), a species of opium poppy that grows in the Holy Land. The person described can bring about the same mental confusion as opium.
Laanah in Hebrew; aklam in Arabic (Saadia; Ibn Janach), exenjos in Old Spanish (Radak, Sherashim). Wormwood (Artemisia absinthium) is an herb yielding a bitter, dark green oil. A paradigm of bitterness, and hence translated merely as ‘bitterness’ (pikra) by the Septuagint.