Entries linking to radically
late 14c., "originating in the root or ground;" of body parts or fluids, "vital to life," from Latin radicalis "of or having roots," from Latin radix (genitive radicis) "root" (from PIE root *wrād- "branch, root"). The basic sense of the word in all meanings is "pertaining or relating to a root or roots," hence "thoroughgoing, extreme."
The figurative meaning "going to the origin, essential" is from 1650s. The political sense of "reformist" is by 1817, of the extreme section of the British Liberal party (radical reform had been a current phrase since 1786), via the notion of "change from the roots" (see radical (n.)). The meaning "unconventional" is from 1921. U.S. youth slang use is from 1983, from 1970s surfer slang meaning "at the limits of control."
The mathematical radical sign, placed before any quantity to denote that its root is to be extracted, is from 1680s; the sign itself is a modification of the letter -r-. Radical chic is attested from 1970; popularized, if not coined, by Tom Wolfe. Radical empiricism was coined 1897 by William James (see empiricism).
common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).
Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.