Fourth Declension
The fourth declension is small but punches above its weight: it owns the vocabulary of action — adventus ("arrival"), cāsus ("fall, chance"), exitus ("outcome"), frūctus ("yield"), impetus ("attack"), senātus, exercitus.
These are verbal nouns built on supine stems with -tus / -sus, so once you know the verb, you can almost predict the noun.
The trap is the nominative singular: a -us ending that looks identical to the second declension. Servus, servī is 2nd; frūctus, frūctūs is 4th. The genitive is the giveaway — and you have to check it every time.
Domus makes things worse by mixing 2nd- and 4th-declension forms in the same word.
The -ūs genitive declension. Mostly masculine (frūctus), a few feminine (manus), four neuter (cornū).
Looks like 2nd declension -us in the nominative. Always confirm with the genitive: 4th = -ūs, 2nd = -ī.
| Case | Singular | Plural |
|---|---|---|
| Nom. | frūct-us | frūct-ūs |
| Gen. | frūct-ūs | frūct-uum |
| Dat. | frūct-uī | frūct-ibus |
| Acc. | frūct-um | frūct-ūs |
| Abl. | frūct-ū | frūct-ibus |
| Case | Singular | Plural |
|---|---|---|
| Nom. | man-us | man-ūs |
| Gen. | man-ūs | man-uum |
| Dat. | man-uī | man-ibus |
| Acc. | man-um | man-ūs |
| Abl. | man-ū | man-ibus |
| Case | Singular | Plural |
|---|---|---|
| Nom. | corn-ū | corn-ua |
| Gen. | corn-ūs | corn-uum |
| Dat. | corn-ū | corn-ibus |
| Acc. | corn-ū | corn-ua |
| Abl. | corn-ū | corn-ibus |
| Case | Singular | Plural |
|---|---|---|
| Nom. | dom-us | dom-ūs |
| Gen. | dom-ūs | dom-uum (dom |
| Dat. | dom-uī (dom | dom-ibus |
| Acc. | dom-um | dom-ōs (dom |
| Abl. | dom-ō (dom | dom-ibus |
| Loc. | dom-ī | — |
See It In Action
— B. G. i. 13
Adventus ("arrival") is the workhorse 4th-declension verbal noun, built from adveniō. Caesar uses it constantly — every army marching anywhere generates an adventus.
— Cic. Cat. i. 25
Manus is feminine (don't be fooled by -us) and means "hand" OR "armed band" — Cicero uses the second sense here. Context decides between the two.
— B. G. i. 25
Impetūs here is accusative plural — direct object of sustinēre. The same form impetūs could be gen. sg. or nom. pl. in another sentence; the syntax tells you which.
domī (locative) — "at home"
domī mīlitiaeque — "at home and on campaign"
domum (acc. without preposition) — "homeward, to home"
domum redīre — "to return home"
domō (abl. without preposition) — "from home"
domō profugere — "to flee from home"
domī meae — "of my house" (gen. sg.)
custōs domī — "the guardian of the house"
everywhere else, domus declines normally — domum aedificāre, in domō
domus alta — "a tall house" (nom. sg., feminine adj.)
Identical in the nominative. Different in everything else. The genitive ending is the only reliable test.
gen. sg. -ūs (long u)
frūctus, frūctūs
fruit — "of the fruit"
gen. sg. -ī
servus, servī
slave — "of the slave"
Tip: Always check the dictionary entry's genitive. Inside a sentence, look at adjective agreement and the surrounding case endings — frūctō doesn't exist (4th abl. = frūctū), and senātī is the rare alternative for senātūs.
You meet fructus, fructūs m. in a dictionary and servus, servī m. in the next entry. Both end in -us. What's the safest way to keep them straight when you read?
Study Tips
- •Memorize manus (F.) and frūctus (M.) side by side — they share endings exactly. Gender is the only difference.
- •Whenever you meet a -us noun in a dictionary, glance at the genitive. -ī means 2nd declension; -ūs means 4th. Don't guess from the nominative.
- •Learn domus as a special creature with its own paradigm. It appears constantly in Caesar and Cicero, and the locative domī ("at home") is one of Latin's most common location idioms.
- •When you hit a -tus / -sus noun, ask: what verb is this from? Adventus ← adveniō, cāsus ← cadō. Recognizing the family doubles your vocabulary at no extra cost.