The word here and in Deuteronomy 32:32 rendered “gall,” is in Hosea 10:4 translated “hemlock.” It is the name of a plant of intense bitterness, and of quick growth; and is therefore repeatedly used in conjunction with “wormwood” (compare Jeremiah 9:15; Lamentations 3:19; Amos 6:12), to express figuratively the nature and effects of sin (compare the marginal references.). The herb is probably the poppy. Hence, the “water” (i. e. juice) “of gall” Jeremiah 8:14; Jeremiah 23:15 would be opium. This would explain its employment in the stupefying drink given to criminals at the time of execution (compare Psalms 69:21; Matthew 27:34), and the use of the word as synonymous with poison (compare Deuteronomy 32:33; Job 20:16).
Wormwood - is the plant “absinthium.” It is used to denote metaphorically the distress and trouble which result from sin.
“The root that beareth gall and wormwood,” means in this place any person lurking among them who is tainted with apostasy.