Modo arbiter pignus tenet, modo victori reddit.

In this sentence, modo ... modo ... means something like at one time ... at another time ..., now ... now ..., or sometimes ... sometimes ....

So:

• Modo arbiter pignus tenet = at one point the judge/arbitrator holds the pledge
• modo victori reddit = at another point he returns it to the winner

This use of modo does not mean only here. Latin modo can have several meanings depending on context, and the repeated pattern modo ... modo ... is a common one.

Arbiter is the subject of the sentence.

It is:

• nominative singular
• a masculine noun of the third declension
• meaning judge, arbiter, or umpire/referee, depending on context

So arbiter ... tenet means the arbiter holds.

Even though arbiter appears only in the first clause, it is also understood as the subject of the second clause:

• modo arbiter pignus tenet
• modo [arbiter] victori reddit

Latin often leaves out a repeated word when it is easy to understand.

Pignus is in the accusative singular, functioning as the direct object of tenet.

So:

• tenet = holds
• pignus = the pledge/stake/security

Together: holds the pledge

A useful thing to notice is that pignus is a neuter third-declension noun, and its nominative singular and accusative singular have the same form: pignus. Here we know it is the object because of the meaning and the verb.

Pignus usually means a pledge, security, token, or stake.

In this sentence, it probably refers to some object being held by the arbiter until the outcome is decided. So depending on the context, you might understand it as:

• pledge
• deposit
• stake
• security

The exact English word can vary, but the idea is that it is something temporarily held and then given back.

Because victori is a dative singular, meaning to the winner, not the winner as a direct object.

The verb reddit means gives back, returns, or hands back, and it often takes:

• a direct object = the thing being returned
• an indirect object in the dative = the person it is returned to

So here the full sense is:

• [arbiter] pignus victori reddit
• the arbiter returns the pledge to the winner

Victorem would be accusative, which would suggest the winner was the direct object, and that would not fit the meaning here.

Victori is the dative singular of victor, meaning winner or conqueror.

So:

• nominative: victor = the winner
• dative: victori = to/for the winner

In this sentence it is the indirect object of reddit.

Reddit comes from the verb reddo, reddere, reddidi, redditum, meaning:

• give back
• return
• restore
• sometimes simply hand over

Here reddit is:

• 3rd person singular
• present active indicative

So it means he/she/it gives back or returns.

Since the subject is arbiter, the translation is the arbiter returns.

You can also notice that reddo is historically related to re- + do (give back), which helps explain the meaning.

Because Latin often omits words that are easily understood from the context.

In English, we might naturally repeat the subject:

• At one time the arbiter holds the pledge, at another time the arbiter returns it to the winner.

But Latin prefers brevity when the meaning is clear:

• Modo arbiter pignus tenet, modo victori reddit.

The second clause still has the same subject, arbiter, understood from the first clause.

It is understood, not stated.

From the first clause, we know the thing being discussed is pignus. So in the second clause, Latin leaves it out because it is obvious:

• modo arbiter pignus tenet
• modo [arbiter] [pignus] victori reddit

In fuller English, that would be:

• at one time the arbiter holds the pledge, at another time he returns the pledge to the winner

Latin often omits repeated objects just as it omits repeated subjects.

Latin word order is more flexible than English word order because Latin uses case endings to show grammatical relationships.

English relies heavily on word order:

• The arbiter returns the pledge to the winner

Latin can arrange words in different ways because forms like victori already show their function. So:

• victori reddit literally looks like to the winner he returns
• but it naturally means he returns it to the winner

The placement of victori before reddit may give slight emphasis to the recipient, but often it is simply natural Latin style rather than something dramatic.

Both tenet and reddit are present indicative forms.

Latin often uses the present tense for actions that are:

• generally true
• repeated
• customary
• vividly described

Here the sentence seems to describe a general or repeated procedure:

• first the arbiter holds the pledge
• then he returns it to the winner

So the present tense can be understood almost like an English general present:

• the arbiter holds ... and returns ...

Yes. In this sentence, modo is an adverb.

Repeated adverbs often create paired expressions in Latin, and modo ... modo ... is one of them. It marks an alternation or sequence of states/actions:

• at one time ... at another
• now ... now

So it is not modifying a noun; it is modifying the clause as a whole.

Yes. Depending on how literally or smoothly you want to translate it, you could say:

• At one time the arbiter holds the pledge, at another he returns it to the winner.
• Now the arbiter keeps the stake, now he gives it back to the winner.
• Sometimes the arbiter holds the pledge, sometimes he returns it to the victor.

The exact English wording depends on context, especially for:

• arbiter = arbiter, judge, referee
• pignus = pledge, stake, security
• victor/victori = winner, victor

But grammatically, the Latin structure stays the same.