La retenue réduit la caution.

Yes. This sentence uses the very common French pattern:

subject + verb + object

• La retenue = the subject
• réduit = the verb
• la caution = the object

So the structure works much like English: The deduction/withholding reduces the deposit/bond.

Because both retenue and caution are feminine singular nouns.

• la retenue
• la caution

In French, the definite article must match the noun’s gender and number. Since both nouns are feminine singular, both take la.

Retenue can have several meanings in French, so context matters a lot.

Common meanings include:

• deduction
• withholding
• amount kept back
• self-restraint or reserve in other contexts

In this sentence, because it is paired with caution, it most likely has a financial or administrative meaning such as deduction or withholding, not self-restraint.

Usually, no. This is an important false friend.

French caution often means:

• deposit
• security deposit
• bond
• guarantee/surety, depending on context

It usually does not mean English caution in the sense of carefulness or warning.

So a learner should be careful not to assume the English meaning automatically.

Because réduire is the infinitive form, meaning to reduce.

In the sentence, the verb must be conjugated to match the subject la retenue, which is third person singular. So:

• réduire = to reduce
• il/elle réduit = he/she/it reduces

Since la retenue is grammatically like it, the correct form is réduit.

Because in French, a conjugated verb does not agree in gender with its subject.

So even though retenue is feminine, the present-tense verb stays:

• la retenue réduit

You would only see gender agreement on things like:

• adjectives
• some past participles, depending on the grammar structure

But not on a normal present-tense verb like réduit.

The accent in réduit is part of the word’s normal spelling, inherited from the verb réduire.

• réduire
• je réduis
• il/elle réduit

That é helps show the correct vowel sound at the beginning of the word, pronounced like ray in a rough English approximation.

So the accent is not optional; it is part of the correct spelling.

A careful pronunciation is approximately:

/la ʁə.tə.ny ʁe.dɥi la ko.sjɔ̃/

A rough English-style guide would be:

lah ruh-tuh-NUE ray-DWEE lah koh-SYON

A few pronunciation notes:

• r in French is a French r, not an English one
• retenue ends with -nue, pronounced ny
• réduit sounds like ray-dwee
• caution ends with a nasal sound, not a fully pronounced English on

Yes, if you wanted an indefinite meaning instead of a definite one.

Compare:

• La retenue réduit la caution = the deduction reduces the deposit
• Une retenue réduit une caution = a deduction reduces a deposit

Using la suggests that the speaker has a specific deduction and a specific deposit/bond in mind.

Definitely. Both key nouns are somewhat context-dependent.

Possible interpretations include things like:

• The deduction reduces the deposit
• The withholding reduces the security deposit
• The deduction lowers the bond
• The amount retained reduces the guarantee

So even if the basic grammar is simple, the exact translation can change depending on whether the context is:

• renting
• banking
• legal matters
• payroll/accounting
• administrative paperwork