a. A final stem-vowel of the first member of the compound usually disappears before a vowel, and usually takes the form of i before a consonant. Only the second member receives inflection.[1][The second part generally has its usual inflection; but, as this kind of composition is in fact older than inflection, the compounded stem sometimes has an inflection of its own (as, cornicen, -cinis; lúcifer, -ferí; iúdex, -dicis), from stems not occurring in Latin. Especially do compound adjectives in Latin take the form of i-stems: as, animus, exanimis; nórma, abnórmis (see § 73). In composition, stems regularly have their uninflected form: as, ígni-spicium, divining by fire. But in o- and á-stems the final vowel of the stem appears as i-, as in áli-pés (from ála, stem álá-); and i- is so common a termination of compounded stems, that it is often added to stems which do not properly have it: as, flóri-comus, flower-crowned (from flós, flór-is, and coma, hair).]
b. Only noun-stems can be thus compounded. A preposition, however, often becomes attached to a verb.