Avus omnium prudentissimus est.

Because avus is the subject of the sentence: it is the person being described as most prudent.

• avus = grandfather
• nominative singular = the grandfather as subject

So in Avus omnium prudentissimus est, avus is the one who is something.

Omnium is the genitive plural of omnis, meaning of all.

With a superlative like prudentissimus (most prudent), Latin often uses the genitive plural to show the group being compared:

• omnium = of all
• prudentissimus omnium = the most prudent of all

So the genitive answers the question most prudent of whom? → of all.

Prudentissimus is the superlative form of prudens (prudent, wise, sensible).

A common way to make a superlative in Latin is:

• adjective stem + -issimus, -a, -um

So:

• prudens → stem prudent-
• prudent-
  • -issimus → prudentissimus

It means most prudent or very prudent, depending on context. In this sentence, because of omnium, it clearly means most prudent.

Because it agrees with avus.

Since avus is:

• masculine
• singular
• nominative

the adjective describing it must also be:

• masculine
• singular
• nominative

So we get prudentissimus, not prudentissima or prudentissimum.

This is standard Latin adjective agreement.

Est is the third person singular present of esse, meaning to be.

So:

• est = is

The sentence structure is:

• Avus = subject
• prudentissimus = predicate adjective
• est = linking verb

So literally: Grandfather is most prudent of all.

Because classical Latin has no definite or indefinite article.

So Latin does not normally use separate words for:

• the
• a
• an

Whether you translate avus as grandfather, the grandfather, or a grandfather depends on context. In a sentence like this, English usually wants the or a possessive like my, but Latin does not have to express that.

Latin word order is much more flexible than English word order.

This sentence could be rearranged without changing the basic meaning, for example:

• Avus omnium prudentissimus est
• Avus prudentissimus omnium est
• Omnium avus prudentissimus est

The chosen order may sound natural or give slight emphasis, but the grammar is shown mainly by the word endings, not by position.

It is being used predicatively.

That means it is not simply attached directly to the noun as in the most prudent grandfather, but is linked to the subject by est:

• Avus ... prudentissimus est = Grandfather is the most prudent

So prudentissimus is a predicate adjective.

Yes, in some contexts a Latin superlative can have an absolute sense, meaning something like:

• very prudent
• extremely prudent

But here omnium makes the meaning clearly relative:

• prudentissimus omnium = the most prudent of all

So in this sentence, most prudent is the right understanding.

No. Omnium is the genitive plural form used for all in a general sense, and the exact group depends on context.

It can refer to:

• all people
• all family members
• all individuals in some group
• even all things, in other contexts

So here it simply means of all; the sentence itself does not specify the group more precisely.

A very literal breakdown is:

• Avus = grandfather
• omnium = of all
• prudentissimus = most prudent
• est = is

So, word for word:

Grandfather of all most prudent is.

Natural English would be:

Grandfather is the most prudent of all.

Because superlatives in Latin commonly take a genitive of the whole:

• doctissimus omnium = the most learned of all
• fortissimus omnium = the bravest of all

So omnium naturally goes with prudentissimus as the comparison group.

If it went with avus, the meaning would be much less natural: grandfather of all. That is possible in some other context, but here the superlative construction makes the intended relationship clear.