Nisi feles prope cellarium vigilat, mus iterum ad nuces venit.

Nisi means unless, or more literally if not. It introduces a condition that limits or blocks what happens in the main clause.

So the structure is:

• Nisi ... = Unless ...
• mus iterum ad nuces venit = the main action

In other words, the mouse comes back to the nuts except when the cat is keeping watch.

Feles is the nominative singular form, which is the form used for the subject of the verb.

Here feles is the subject of vigilat, so nominative is exactly what we expect.

This noun belongs to the third declension. Its dictionary form is typically given as feles, felis.

Because prope is a preposition that takes the accusative case when it means near.

So:

• prope = near
• cellarium = accusative singular

Together, prope cellarium means near the pantry/store-room.

This is something English speakers often have to get used to: in Latin, prepositions usually require a specific case.

Vigilat is the 3rd person singular present active indicative of vigilare.

It can mean things like:

• is awake
• keeps watch
• stands guard
• is watching

In this sentence, keeps watch or stands guard fits especially well, because the cat’s watchfulness affects whether the mouse dares to come back.

Mus is the nominative singular form, so it is used because the mouse is the subject of venit.

The noun is mus, muris. Like many third-declension nouns, its nominative form can look quite different from the rest of the stem:

• nominative singular: mus
• genitive singular: muris

A learner often expects something closer to mur-, but the nominative singular is simply mus.

Iterum is an adverb meaning again.

It tells you that the mouse’s action is repeated: the mouse comes again.

Latin adverbs are often quite movable, so iterum could appear in a different place and still modify the action of coming. Here it sits naturally before ad nuces venit.

Because ad means to or toward, and it takes the accusative case.

So:

• ad = to, toward
• nuces = accusative plural of nux, nucis = nut

That gives ad nuces = to the nuts.

The plural nuces suggests there is a pile or supply of nuts, not just one nut.

Yes — that is a very common question.

Without macrons, venit can represent either:

• venit = he/she/it comes (present)
• vēnit = he/she/it came / has come (perfect)

In fully marked Latin, the perfect has a long ē: vēnit. But many printed texts do not show macrons, so the form looks ambiguous.

Here, context shows that it is present: the sentence describes a general situation or repeated behavior, not a one-time past event.

The present tense here expresses a general pattern or habitual situation.

The sentence is not mainly about one single event. It is more like a rule:

• if the cat is not on guard,
• the mouse comes back to the nuts.

Latin, like English, often uses the present tense for this kind of repeated or typical action.

Because this is a simple, straightforward condition, and Latin commonly uses the indicative for that.

So:

• nisi feles prope cellarium vigilat = unless the cat is keeping watch near the pantry

There is nothing especially hypothetical, doubtful, or contrary-to-fact here. It is presented as a normal real condition, so the indicative is perfectly natural.

Latin word order is much more flexible than English word order because Latin endings show what each word is doing.

This sentence starts with the nisi clause first:

• Nisi feles prope cellarium vigilat
• then the main clause: mus iterum ad nuces venit

That ordering makes good sense stylistically because it sets up the condition first. Also, Latin often likes to place verbs toward the end of their clauses, though this is a tendency, not a strict rule.

Latin has no articles. There is no separate word exactly equivalent to English the or a/an.

So a noun like feles can mean:

• the cat
• a cat

and the context tells you which is meant.

The same is true for mus, cellarium, and nuces. English must choose an article, but Latin usually does not say one at all.