/rad"i keuhl/ , n.
1. Bot.
a. the lower part of the axis of an embryo; the primary root. See diag. under plumule .
b. a rudimentary root; radicel or rootlet.
2. Chem. (formerly) radical (def. 12).
3. Anat. a small rootlike part or structure, as the beginning of a nerve or vein.
[ 1665-75; radicula small root, equiv. to radic- (s. of radix ) ROOT 1 + -ula -ULE ]