The root is the primary lexical unit of a word, which carries the most significant aspects of semantic content and cannot be reduced into smaller constituents. Content words in nearly all languages represent root morphemes.

Roots can be either free morphemes or bound morphemes. Root morphemes are essential for affixation and compounds.

The root of a word is a unit of meaning (morpheme) and, as such, it is an abstraction, though it can usually be represented in writing as a word would be. For example, it can be said that the root of the English verb form running is run, or the root of the Spanish superlative adjective amplísimo is ampli-, since those words are clearly derived from the root forms by simple suffixes that do not alter the roots in any way. In particular, English has very little inflection, and hence a tendency to have words that are identical to their roots. But more complicated inflection, as well as other processes, can obscure the root; for example, the root of mice is mouse (still a valid word), and the root of interrupt is, arguably, rupt, which is not a word in English and only appears in derivational forms (such as disrupt, corrupt, etc.). The root rupt is written as if it were a word, but it's not.

This distinction between the word as a unit of speech and the root as a unit of meaning is even more important in the case of languages where roots have many different forms when used in actual words, as is the case in Semitic languages. In these, roots are formed by consonants alone, and different words (belonging to different parts of speech) are derived from the same root by inserting vowels. For example, in Hebrew, the root gdl represents the idea of largeness, and from it we have gadol and gdola (masculine and feminine forms of the adjective "big"), gadal "he grew", higdil "he magnified" and magdelet "magnifier", along with many other words.

Reconstructed roots

The root of a word, in etymology, has a somewhat different meaning: it may represent an older form. When several languages are believed to be children of one older language, linguists will compare each language to the rest, trying to find matching words and ultimately reconstruct the ancient root. This has been done with several major language families, such as the Indo-European and the Semitic family.

See also

• Morphology
• Morphological typology
• Stem
• List of Indo-European roots