[184]. A root is not a real word; it is neither a noun, naming something, nor a verb, denoting action. Thus iug-, yoke, does not mean a yoke nor I yoke; it merely suggests something about yoking. The root becomes a real word only when an inflection ending is added, or, more commonly, both a formative suffix and an inflection ending: as, iug-u-m, a yoke.
[185]. Roots are common to Latin and its cognate languages, such as the Sanskrit and the Greek. When a root is named in this book, the specific Latin form of the root is meant. This often differs somewhat from the form of the root which is assumed as applicable to all the cognate languages.
[186]. Almost all roots are noun and verb roots; that is, roots with a meaning which may be embodied either in a noun or in a verb, or in both. Besides these there is a small class, less than a dozen in number, of pronoun roots. There are many words which cannot be traced back to their roots.
[187]. A root sometimes has two or more forms: as, fīd- (for feid-), foed-, fid-, trust; gen-, gn-, sire; tol, tl, bear; see [135], [145].
Thus, fīd- is found in fīd-us, trusty, fīd-ūcia, confidence, fīd-ūciō, I pledge, fīd-ūciārius, in trust, fīd-ere, put trust in, fīd-ēns, courageous, fīd-entia, courage; foed- in foed-us, pledge of faith, foed-erātus, bound by a pledge of faith; fid- in fid-ēs, faith, fid-ēlis, faithful, fid-ēliter, faithfully, fid-ēlitās, faithfulness, per-fid-us, faithless, per-fid-ia, faithlessness, per-fid-iōsus, full of faithlessness, per-fid-iōsē, faithlessly. gen- in gen-itor, sire, gn- in gi-gn-ere, beget, gn-ā- in gnā-tus, son.
[188]. A root ending in a vowel is called a Vowel Root: as, da-, give; a root ending in a consonant is called a Consonant Root: as, rup-, break. Roots are conveniently indicated by the sign √: as, √teg-, to be read ‘root teg-.’
[189]. A root or a part of a root is sometimes doubled in forming a word; this is called Reduplication: as, mur-mur, murmur; tur-tur, turtle-dove; po-pul-us, people; ul-ul-āre, yell.
[190]. Many nouns are formed from the present stems of verbs, which take the place of roots. Stems thus used are mostly those of verbs in -āre and -īre.
Thus, from ōrā-, stem of ōrāre, speak, are formed ōrā-tor, speaker, and ōrā-tiō, speech; from audī-, stem of audīre, hear, are formed audī-tor, hearer, and audī-tiō, hearing.