Legatum partem hereditatis legatario dat.

Because Latin often leaves the subject pronoun unstated when the verb already tells you the person and number.

Here, dat means he/she/it gives:

• da- = the verb stem from do (give)
• -t = third person singular

So Latin does not need to add is/ea/id unless the speaker wants emphasis or contrast.

Latin has no articles. It does not have separate words that directly match English the or a/an.

So a noun like legatum can mean:

• a legacy
• the legacy

The context decides which English article makes best sense.

Legatario is dative singular.

The dative case is commonly used for the indirect object, especially with verbs of giving, telling, showing, and similar actions.

Since dat means gives, the person receiving something is put in the dative:

• legatario = to the legatee

So this follows a very common Latin pattern:

someone gives something to someone
= subject + accusative direct object + dative indirect object + dat

Hereditatis is genitive singular of hereditas (inheritance).

It depends on partem (part), because Latin often uses the genitive after words like:

• part
• much
• enough
• the rest
• one of

So:

• partem hereditatis = part of the inheritance

This use is often called the partitive genitive or sometimes the genitive of the whole.

That is a very natural question, because English usually makes us expect just one direct object.

Here the most likely explanation is that partem hereditatis is in apposition to legatum. Apposition means one noun explains, renames, or identifies another noun, and both stay in the same case.

So the sense is like:

• legatum, partem hereditatis
• a legacy, that is, a part of the inheritance

Both are therefore accusative because they belong to the same object idea.

Latin often does this more compactly than English.

Formally, yes.

Because legatum is a second-declension neuter noun, its nominative singular and accusative singular look the same:

• nominative singular: legatum
• accusative singular: legatum

So just from the form alone, you cannot tell which case it is.

You have to use:

• the meaning,
• the syntax,
• and the wider context.

In this teaching sentence, it is most naturally taken as an accusative noun linked with partem hereditatis. But the ambiguity is real, and noticing it is good Latin reading practice.

Yes, that is very normal.

Latin word order is much freer than English word order because the endings show each word’s job in the sentence. Latin often places the verb at or near the end.

So:

• Legatum partem hereditatis legatario dat.

is perfectly normal Latin ordering.

English depends much more on position:

• He gives a legacy to the legatee
• not usually A legacy to the legatee he gives

Latin can move words around more easily for emphasis, rhythm, or style.

Yes, they are related in origin.

• legatum = legacy, bequest
• legatarius / legatario = legatee, the person who receives a bequest

Both are connected with the idea of something left by will. That is why they look similar.

But grammatically they are different words:

• legatum is the thing given
• legatario is the person receiving it

Here is the breakdown:

• legatum
  from legatum, -i n.
  neuter singular, form can be nominative or accusative

• partem
  from pars, partis f.
  accusative singular

• hereditatis
  from hereditas, hereditatis f.
  genitive singular

• legatario
  from legatarius, -i m.
  dative singular

• dat
  from do, dare, dedi, datum
  third person singular present active indicative
  = gives

This kind of parsing is very useful because Latin meaning depends heavily on endings.

The verb do (give) regularly takes:

• a direct object in the accusative
• an indirect object in the dative

So the core pattern is:

someone gives something to someone

In this sentence:

• the thing given is expressed by the accusative noun phrase
• the recipient is legatario in the dative

That is one of the most basic and important sentence patterns in Latin.