Arising from or going to a root or source; basic, Medicine Relating to or being surgery that is extreme or drastic in an effort to eradicate all existing or potential disease, Proceeding from a rootlike stem, or one which does not rise above the ground, noun_ Specifically, a group of two or more atoms, not completely saturated, which are so linked that their union implies certain properties, and are conveniently regarded as playing the part of a single atom; a residue; -- called also a compound radical. Cf. Residue, A primitive letter; a letter that belongs to the radix, A person who holds or acts according to radical principles; one who pursues a theory to its furthest apparent limit; an extremist, especially in politics