Is it ensure, insure, or assure?
1670s, in botany, from Latin radicula, diminutive of radix (see radish).
radicle rad·i·cle (rād'ĭ-kəl)n. A small structure, such as a fibril of a nerve, that resembles a root.
The part of a plant embryo that develops into a root. In most seeds, the radicle is the first structure to emerge on germination.
A small anatomical structure, such as a fibril of a nerve, that resembles a root.