phthi·o·col \ˈthīəˌkȯl, -kōl\noun (-s) Etymology: probably from phthisis + connective -oc- + -ol : a yellow crystalline quinone C11H8O3 with vitamin K activity that is isolated from the human tubercle bacillus and also made synthetically; 2-hydroxy-3-methyl-1,4-naphthoquinone