(a). A Primary word is one which requires no additional letters to give it a distinct meaning (see list of Primary Words, [Part V]).
(b). A Simple word is one formed by adding a grammatical termination to a single root, or to a primary word (which then becomes a root), with or without suffixes or prefixes.
Examples.—Bon-a = Good. Ĉirkaŭ-i = To surround. Antaŭ-ul-o = A predecessor. Dis-sem-i = To scatter. Mal-san-ul-ejo = An infirmary.
(c). A Compound word is one formed by adding a grammatical termination to two or more roots, or to a primary word and a root, with or without suffixes or prefixes. Any of the component parts may be complete words, if euphony requires it.
Examples.—Bon-intenc-a = Well-meaning. Super-natur-a = Supernatural. Antaŭ-vid-i = To foresee. Ĉas-o-ŝtel-ist-o = A poacher. Ĉas-gard-ist-o = A gamekeeper. Vapor-ŝipo = A steamship. Griz-har-a = Grey-haired. Super-akv-eg-o = A deluge.
(d). A Foreign word is one common to most languages, being derived from the same root.
Examples.—Teatr-o = Theatre. Teatr-a = Theatrical. Geologi-o = Geology. Geologi-a = Geological.
FORMATION OF WORDS (Vortfarado).
40. To show the manner in which words are formed in Esperanto, it will perhaps be better first to do so in Dr. Zamenhof’s own words, as given on page 248 of his "Fundamenta Krestomatio." He says:—
"I arranged a complete dismemberment of ideas into independent words, so that the whole language, instead of being words in various grammatical forms, consists solely of unchangeable words. If you will take a work written in my language, you will find that each word is always in one constant form, namely, in that form in which it is printed in the dictionary, and that the various grammatical forms, reciprocal relation between words, etc., etc., are expressed by the union of unchanging words. But, because such a construction of language is quite strange to Europeans, I adapted this dismemberment of the language to the spirit of the European languages, so that anyone learning mine from a manual would not suppose that it differed in construction from his own. Take, for example, the word fratino, which in reality consists of three words, frat, in, o. Frat gives the idea of the offspring[9] of one’s parents, in the idea of the female sex, and o the idea of existence (person or thing), hence a noun. These three ideas combined, in Esperanto, make fratino = a sister. The first and last make frato = a brother. The instruction book shows this in the following manner:—Brother = frat-, but because every substantive in the nominative ends in o, therefore frato = brother. For the formation of the feminine, the little word -in- is inserted, therefore fratino = sister. In this way, the dismemberment of the language in no way embarrasses the learner; he does not even suspect that that which he calls a prefix, or suffix, or termination, is really an independent word, which always preserves its meaning, no matter whether it be used at the beginning, middle, or end of a word, or independently, and that every word, with equal right, can be used as a root word or grammatical particle."