Dolium olearium oleum viride habet.

• dolium = jar, cask, barrel
• olearium = for oil, oil-related
• oleum = oil
• viride = green
• habet = has

So the sentence breaks into two noun phrases plus a verb:

• dolium olearium = an oil jar / a jar for oil
• oleum viride = green oil
• habet = has

That gives the sense The oil jar has green oil.

They come from the same oil-related root.

• oleum is the noun meaning oil
• olearium is an adjective meaning of oil, for oil, or oil-related

So dolium olearium is literally something like an oil-related jar, which English would normally say as oil jar or jar for oil.

Because both are second-declension neuter singular nouns.

In that declension, the nominative singular and accusative singular have the same ending: -um.

So:

• dolium can be nominative singular or accusative singular
• oleum can also be nominative singular or accusative singular

That is very normal for neuter nouns in Latin.

Mostly from word order and sense.

A reader will normally take:

• dolium olearium as the subject phrase
• oleum viride as the object phrase
• habet as the verb

So the natural reading is The oil jar has green oil.

However, from endings alone, the sentence is not perfectly disambiguated, because both dolium and oleum could in theory be nominative or accusative. This is one of those cases where Latin relies on context and normal phrasing.

Because they belong to different adjective patterns.

• olearium comes from olearius, olearia, olearium, a first-and-second-declension adjective
• viride comes from viridis, viridis, viride, a third-declension adjective

Both adjectives still agree with the nouns they describe in gender, number, and case:

• olearium agrees with dolium
• viride agrees with oleum

They just show that agreement with different endings because they come from different adjective classes.

Yes, it is an adjective modifying dolium.

Latin often uses noun + adjective where English prefers a compound noun. So:

• dolium olearium literally = oil-related jar
• natural English = oil jar

This is a very common difference between Latin and English.

Habet is:

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

It comes from habere, meaning to have.

So habet means he has, she has, or it has. Here it means it has, because the subject is dolium, a thing.

Because classical Latin does not have articles like English the and a/an.

So dolium can mean:

• a jar
• the jar

And oleum can mean:

• oil
• the oil
• sometimes even some oil

The exact choice depends on context and on what meaning has already been given to the learner.

Yes. It is a very straightforward beginner-style Latin sentence.

The pattern is:

• noun + adjective
• noun + adjective
• verb at the end

So:

• dolium olearium
• oleum viride
• habet

That is perfectly natural Latin style. Latin word order is more flexible than English, but in this sentence the chosen order makes the structure easy to follow.

Sometimes yes, but here you have to be careful.

Latin often allows different word orders, especially because endings show grammatical function. But in this sentence, the two nouns are both neuter singular forms that can look like either subject or object. That means word order helps a lot.

So a rearrangement such as Dolium olearium habet oleum viride would still likely be understood the same way, but a more drastic change could make the sentence harder to interpret or even suggest a different subject.

In other words:

• Latin is flexible
• but this particular sentence has some built-in ambiguity
• so the given order is especially helpful for the reader