IMPARASYLLABIC NOUNS OF THE OF THE THIRD DECLENSION AND EXCEPTIONS TO THE RULES FOR THE QUANTITY OF FINAL SYLLABLES IN LATIN

Imparasyllabic nouns are those which have one more syllable in their Genitive Singulars than in their Nominative Singulars. The majority of such nouns are in the Third Declension, and within this declension there are two groups, or categories, of nouns (and related adjectives) which are of significance in relation to the length of syllables at the end of words, i.e. final syllables: 

1) Imparasyllabic Third Declension nouns with nominative Singulars ending in '- es', which have a short penultimate syllable in the Genitive Singular. In almost all Latin words ending in '- es', that syllable is pronounced long. However, in the case of this group of nouns, the final '- es' is short. Such nouns, and related adjectives, are listed below:  

ales, alitis.  c. bird, omen.  adj. winged, swift.  

caeles, caelitis.  adj. celestial. m.pl. the gods.

caespes, caespitis. m. sod, turf, mass of  roots

comes, comitis.  c. companion, partner, attendant, follower

dives, divitis.  adj. rich, wealthy, plentiful.

eques, equitis.  m. horseman, cavalryman, knight. 

gurges, gurgitis. m. deep water, abyss, flood, spendthrift.

hebes, hebetis. adj. blunt, dull, sluggish, stupid.

hospes, hospitis.  m. host, guest, stranger, foreigner.

limes, limitis. m. path, boundary, track, way, frontier

merges, mergitis.  f. sheaf (of corn).

miles, militis.  m. soldier. 

mollipes, mollipedis.  adj. soft-footed.

obses, obsidis.  f. hostage, guarantee.

palmes, palmitis.  m. branch, vine-shoot

pedes, peditis.  m. foot-soldier, infantryman.

poples, poplitis. m. knee, ham, hough.

praepes, praepetis.  f. bird.  adj. swift, winged, of good omen.

praeses, praesidis.  m. guardian, president, chief.  adj. presiding, protecting.

praestes, praestitis.  m. protector, guardian.  adj. protecting.

reses, residis.  adj. lazy, inactive.

satelles, satellitis. c. attendant, follower, courtier, life-guard, accomplice.

seges, segetis. f. cornfield, crop.

sospes, sospitis.  m. saviour, preserver, deliverer.  adj. safe, unhurt, favourable. 

stipes, stipitis.  m. log, tree, stump, trunk of a tree.

superstes, superstitis.  c. by-stander, witness, survivor.  adj. standing by, surviving, remaining.  

teges, tegetis. f. mat.

teres, teretis.  adj. rounded, smooth, polished, elegant. 

termes, termitis. m. branch.

trames, tramitis. m. footpath, path, by-way.

veles, velitis. m. light-armed soldier, skirmisher.

(N.B. In the case of all these above words, I suspect that, when we read them in prose, we often err by pronouncing the final '-es' syllable long. At the same time, I fear we also pronounce the final 's' like a 'z', as in English 'rose'. In Latin, however, 's' is always pronounced with a hissing sound, as in English 'sit'. So, for instance, 'comes' should always be pronounced 'commess', not 'commeyz'.) 

In the case of this group of Third Declension words, there are, inevitably perhaps, some exceptions to the exceptions. In the case of the following words which end in '- ies', their Nominative Singulars end in a long syllable, even though the penultimate syllables of their Genitive Singulars are pronounced short:

abies, abietis.  f. fir-tree, ship, spear, writing-tablet.

aries, arietis.  m. ram, battering-ram.

paries, parietis.  m. wall of a building. 

Another anomaly is the monosyllabic noun pes, pedis. m. foot, and its adjectival derivatives, bipes, bipedis; tripes, tripedis; and quadrupes, quadrupedis. Although these are imparasyllabic and have Genitive Singulars with a short penultimate syllable, the Nominative Singular of pes, and the final syllable of the Nominative Singulars of its derivatives are pronounced long, unlike the final syllable of the Nominative Singulars of mollipes and pedes (listed above), which are pronounced short - very confusing!

Further anomalies are heres, heredis. c. heir, heiress; and lebes, lebetis. m. copper basin, cauldron. Although both of these words are imparasyllabic, and the final syllables of their Nominative Singulars are short (N.B. a number of Latin dictionaries err in showing them as long), the penultimate syllable of their Genitive Singulars is long in both cases. However, while these two words share that characteristic, they differ in that the initial syllable of heres is long and that of lebes short.

2) Imparasyllabic Third Declension Nouns with Nominative Singulars ending in '- us', which have a long penultimate syllable in the Genitive Singular. In almost all Latin words ending in '-us', this syllable is pronounced short. However, in the case of this second group of nouns, the final '- us' is pronounced long. Such nouns are listed below:

crus, cruris. n. leg, shin.

incus, incudis.  f. anvil.

iuventus, iuventutis.  f. youth, manhood, men, soldiers.

palus, paludis.  f. marsh, pool, lake.

rus, ruris.  n. country, countryside, farm, estate.

salus, salutis. f. safety, health.

senectus, senectutis. old age, old men.

servitus, servitutis. f. slavery, service.

tellus, telluris.  f. earth, ground, land, country.

tus, turis.  n. incense, frankincense, spice.

virtus, virtutis.  f. virtue, courage, valour, manhood, strength, prowess.

Conclusion.  These two groups of Third Declension words are almost geometrically opposed to each other in terms of their characteristics and significance. The first group has Nominative Singulars which are pronounced short, and the second group has Nominative Singulars which are pronounced long. In the first group the penultimate syllable of the Genitive Singular is short; in the second group it is long. The first group has the effect of shortening an ending ('- es') which is otherwise almost always pronounced long, and the second group has the effect of lengthening an ending ('-us') which is otherwise almost always pronounced short. In both cases, however, it is particularly necessary to remember these details when scanning verse.