Easton's Bible Dictionary
(1.) Hebrews rosh (Hosea 10:4; rendered "gall" in Deuteronomy 29:18; 32:32; Psalm 69:21; Jeremiah 9:15; 23:15; "poison, " Job 20:16; "venom, " Deuteronomy 32:33). "Rosh is the name of some poisonous plant which grows quickly and luxuriantly; of a bitter taste, and therefore coupled with wormwood (Deuteronomy 29:18; Lamentations 3:19). Hence it would seem to be not the hemlock cicuta, nor the colocynth or wild gourd, nor lolium darnel, but the poppy so called from its heads" (Gesenius, Lex.).
(2.) Hebrews la'anah, generally rendered "wormwood" (q.v.), Deuteronomy 29:18, Text 17; Proverbs 5:4; Jeremiah 9:15; 23:15. Once it is rendered "hemlock" (Amos 6:12; R.V., "wormwood"). This Hebrew word is from a root meaning "to curse," hence the accursed.
Noah Webster's New International Dictionary of the English Language
1. (n.) The name of several poisonous umbelliferous herbs having finely cut leaves and small white flowers, as the Cicuta maculata, bulbifera, and virosa, and the Conium maculatum. See Conium.
2. (n.) An evergreen tree common in North America (Abies, / Tsuga, Canadensis); hemlock spruce.
3. (n.) The wood or timber of the hemlock tree.