Puella annulum retinet, donec mater domum redeat.

Because puella is the subject of retinet. It is the one doing the action: the girl keeps/holds onto the ring.

In Latin, the subject is usually put in the nominative case.
So:

• puella = the girl (nominative, subject)

Because annulum is the direct object of retinet. It is the thing being kept or held.

Latin uses the accusative for the direct object.
So:

• annulus = ring (dictionary form, nominative singular)
• annulum = ring (accusative singular, direct object)

This shows that the sentence means the girl is keeping the ring, not that the ring is doing something.

Retinet comes from retinere, meaning to hold back, keep, retain, keep possession of.

Here it is:

• 3rd person singular
• present tense
• active voice
• indicative mood

So retinet means she keeps, she is keeping, or she retains, depending on how naturally you want to translate it in English.

Because mater is the subject of the second verb, redeat.

Even though English might not make this very noticeable, Latin has a separate clause after donec:

• main clause: Puella annulum retinet
• subordinate clause: donec mater domum redeat

In that subordinate clause, mater is the one doing the action of returning, so it is nominative.

Because domum is part of a very common Latin idiom. With words like domus (home/house), Latin often uses the accusative without a preposition to express motion toward.

So:

• domum = home, to home, homeward

This is similar to English, where we say go home, not usually go to home.

So mater domum redeat means the mother returns home.

Because after donec, Latin can use the subjunctive when the action is viewed as anticipated, expected, or still in the future from the standpoint of the main clause.

So here:

• Puella annulum retinet = the girl keeps the ring
• donec mater domum redeat = until her mother comes back home

The return of the mother is not being presented as a simple factual event already reached; it is the point up to which the girl keeps the ring. That is why redeat is in the present subjunctive.

Yes, but it would change the nuance.

• redit = returns / is returning (indicative)
• redeat = may return / should return / returns in a subordinate clause with a more prospective or dependent sense

After donec, the indicative often gives a more straightforward factual sense, while the subjunctive often gives a sense of expectation, purpose-like anticipation, or an event still pending.

So redeat is not random; it helps express the idea until the mother comes back as a future limit of the main action.

It is a subordinate clause of time, introduced by donec, meaning until.

The clause tells us how long the action in the main clause lasts:

• The girl keeps the ring
• until the mother returns home

So the donec clause sets the endpoint of the action.

Latin often uses the present subjunctive in subordinate clauses when the action is future relative to the main verb and is seen as not yet realized.

So redeat does not have to mean present time in the English sense. In this kind of clause, it can refer to something that will happen.

That is why English may translate it naturally as:

• until the mother returns home
• or even until the mother comes back home

Yes, but it is normal Latin word order rather than something unusual.

Latin word order is more flexible than English because case endings show grammatical function. Here the sentence is arranged quite naturally:

• Puella — subject first
• annulum — object next
• retinet — verb at the end of the main clause
• then the donec clause follows

In the subordinate clause:

• mater — subject
• domum — destination
• redeat — verb at the end

Putting the verb at the end of each clause is a very common Latin pattern.

You know mainly from the case endings and the verb forms, not just from position.

• puella is nominative, so it is the subject of retinet
• annulum is accusative, so it is the object of retinet
• mater is nominative, so it is the subject of redeat
• domum is accusative of motion toward place, so it shows destination

So even if the word order changed, the endings would still tell you the structure.

They are:

• puella, puellae — girl
• annulus, annuli — ring
• retineo, retinere, retinui, retentus — hold back, keep, retain
• donec — until
• mater, matris — mother
• domus, domus (sometimes with mixed forms) — home, house
• redeo, redire, redii/redii, reditus — go back, return

Knowing the dictionary form helps you identify why the forms in the sentence look the way they do.

Yes, redeat includes the idea of back because it comes from redeo:

• re- = back
• eo = go

So redeo literally means go back or return.

Then domum redeat is something like go back home or simply return home. In natural English, return home is usually the smoothest translation.