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 ampl-, 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, rupture, 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 such as godel "size" and migdal "tower".
"Consider Israeli Hebrew מיקום mikúm ‘locating’, from Israeli Hebrew מקמ √mqm ‘locate’, which derives from Biblical Hebrew מקום måqom ‘place’, whose root is קומ √qwm ‘stand’. A recent example introduced by the Academy of the Hebrew Language is מדרוג midrúg ‘rating’, from מדרג midrág, whose root is דרג √drg ‘grade’.
"Consider also Rabbinic Hebrew תרמ √trm ‘donate, contribute’ (Mishnah: T’rumoth 1:2: ‘separate priestly dues’), which derives from Biblical Hebrew תרומה t'rūmå ‘contribution’, whose root is רומ √rwm ‘raise’; cf. Rabbinic Hebrew תרע √tr` ‘sound the trumpet, blow the horn’, from Biblical Hebrew תרועה t'rū`å ‘shout, cry, loud sound, trumpet-call’, in turn from רוע √rw`.
"Similar cases occur in Arabic, e.g.