ROOT.
1. Also sometimes radical. In traditional GRAMMAR and PHILOLOGY, the element, often monosyllabic, left after all affixes have been removed from a complex WORD: -ceive in receive, help in unhelpfully, act in reactivation. A root may or may not be a word, and may have several forms and meanings the further back it is traced in a language or languages. Compare BASE
.
2. Also ROOT-WORD. A word that is ancestral to a present-day word: the Latin verb decidere, the root of the English verb decide and the French verb décider. Compare ETYMON. The classical elements in the vocabulary of English have often been listed and discussed, especially in textbooks and dictionaries, as ‘LATIN and GREEK roots’, sometimes in the first sense given here, sometimes in the second sense, sometimes as a mix of the two.

In LINGUISTICS, a distinction is generally made not only between the two senses of root (above) but also between the terms root and base. The Latin nescius is the root or source of English nice, but is not a root in the philological sense. Rather, it consists of two elements, ne not, scius knowing. Its form cannot be detected anywhere ‘inside’ or ‘under’ present-day nice, which serves as a base for the formations nicety and niceness. Ne is a particle that also appears in neuter, and scius is made up of a linguistic root sci and an inflectional ending -us. Sci is present in the Latin scientia and its English derivative science; it is ancient, being the Latin ‘descendant’ of the Indo-European root *skei to cut, split. This ‘deep’ primoridial root also appears to underlie Old English scinu (Modern English shin), Old High German scina needle, Old Irish scian knife, Greek schizein to split, and Latin scindere to cut. See INDO-EUROPEAN ROOTS, ROOT-CREATION, WORD-FORMATION.