Iudex de gravi facinore discit.

Because iudex is a third-declension noun, not a second-declension one.

Its dictionary form is iudex, iudicis and it means judge. In this sentence, iudex is nominative singular, so it is the subject: the judge is the one doing the action.

A learner often expects the subject to look like dominus or servus, but many Latin subjects do not end in -us. Third-declension nouns have a wider variety of nominative endings, and -ex is one of them.

De gravi facinore is in the ablative because the preposition de takes the ablative.

So:

• de = about / concerning
• gravi facinore = ablative singular

Latin prepositions often control a specific case. Here, de must be followed by the ablative, so both the noun and its adjective appear in the ablative:

• gravi = ablative singular
• facinore = ablative singular

Because after de, the noun phrase must be in the ablative singular.

The noun is facinus, facinoris, a neuter third-declension noun meaning crime, deed, or often wicked deed / crime depending on context.

Its forms here are:

• nominative singular: facinus
• ablative singular: facinore

The adjective gravis, grave must agree with the noun in case, number, and gender, so with facinore it becomes:

• gravi = ablative singular, agreeing with facinore

So de gravi facinore means about a serious crime.

Because gravis, grave is a third-declension adjective, and here it is ablative singular to match facinore.

Agreement is the key idea:

• facinore = ablative singular, neuter
• gravi = ablative singular, neuter

In the ablative singular of many third-declension adjectives, you often see -i.

So gravi is not a strange separate word; it is simply the correct form of gravis used with facinore.

Discit is from disco, discere, didici and means learns or is learning.

It is:

• third person singular
• present tense
• active voice
• indicative mood

So discit means he/she/it learns or is learning.
Because the subject is iudex, the full sense is the judge learns or the judge is learning.

Depending on context, English may translate the Latin present as either simple present or progressive:

• learns
• is learning

Latin has no articles like English the or a/an.

That means iudex can mean:

• the judge
• a judge

And gravi facinore can mean:

• about a serious crime
• about the serious crime

The exact English article depends on context. In isolated teaching sentences, English usually adds the most natural article, but Latin itself does not mark that distinction directly.

Yes, but it would mean something a little different in structure.

• Iudex de gravi facinore discit = The judge learns about a serious crime
• Iudex grave facinus discit = The judge learns a serious crime / learns of a serious crime

The version with de + ablative clearly gives the sense about / concerning.
The version without de uses grave facinus as a more direct object.

A beginner should learn that disco can appear with different constructions, and the wording can slightly shift the nuance.

Yes, it could be rearranged, because Latin word order is more flexible than English word order.

For example, these would still mean roughly the same thing:

• Iudex de gravi facinore discit
• De gravi facinore iudex discit
• Discit iudex de gravi facinore

The case endings show what each word is doing, so Latin does not rely on word order as heavily as English does.

That said, word order can affect emphasis:

• putting discit first may emphasize the action
• putting de gravi facinore first may emphasize the topic
• the given order is a straightforward, neutral arrangement

Facinus is a third-declension neuter noun.

Its principal forms are:

• nominative singular: facinus
• genitive singular: facinoris

From the genitive facinoris, you can see the stem facinor-. That stem is used in most of the oblique cases, including the ablative singular:

• nominative singular: facinus
• ablative singular: facinore

This is why the form changes so much. In third-declension nouns, the nominative singular is often less predictable, so learners should always pay attention to the genitive form in the dictionary.

A common classroom pronunciation would be roughly:

YOO-deks deh GRAH-wee fah-kee-NO-reh DIS-kit

More traditionally reconstructed Classical pronunciation:

• iudex = YOO-deks
• de = deh
• gravi = GRAH-wee
• facinore = fah-kih-NO-reh
• discit = DIS-kit

A few helpful points:

• Latin i at the start of iudex sounds like English y
• c in classical Latin is always hard, so discit sounds like dis-kit, not dish-it
• v in reconstructed Classical Latin is closer to w, though many classrooms pronounce it like English v

Not always. Gravis has a range of meanings, including:

• heavy
• serious
• grave
• weighty
• severe

In de gravi facinore, the most natural meaning is serious or grave, because the noun is crime. So the phrase suggests a serious crime or grave offense.

Latin adjectives often have a broader range than one single English word, so the best translation depends on context.