[174]. The final syllable of the first member of compounds ([181]) sometimes undergoes certain changes by analogy to other compounds:
([1.]) The final -ā of ā-stems, by analogy to the more frequent -o-stems, usually changed to -o, which in atonic syllables became -i ([105]): as, āli-ger, winged, for *ālo-ger from ālā-.
([2.]) Stems in -on- substitute -o- for -on- by analogy to the -o-stems: as, homi-cída, murderer, for *homo-cīda ([105]) from homon- (Nom. homō).
([3.]) Some stems in -s substitute -o- by analogy to the -o-stems: as, foedi-fragus, treaty-breaking, for *foedo-fragus from the stem foedos- (Nom. foedus, Gen. foederis; 154).
[SYLLABLES.]
[175]. A word has as many syllables as it has separate vowels or diphthongs. The last syllable is called the Ultima; the last syllable but one is called the Penult; the last syllable but two is called the Antepenult.
[176]. The quantity of single sounds (e.g. the quantity of a vowel) must be carefully distinguished from the quantity of the group of sounds or the syllable of which the single sound forms a part.
[LENGTH OF SYLLABLES.]
[177]. A syllable is long if its vowel is long, or if its vowel is followed by two consonants or by x or z: as,
dūcēbās; volvunt. In dūcēbās both the vowels and the syllables are long; in volvunt the vowels are short, but the syllables are long; in cases like the last the syllables (not the vowels) are said to be long by position. h does not count as a consonant ([58]) and qu (or qv, [27]) has the value of a single consonant only: thus, in adhūc and aqua the first syllable is short.