Pactum summam dotis continet.

The subject is pactum.

Here, continet is a singular verb, so we look for a singular nominative noun to match it. Pactum is nominative singular neuter, so it means the agreement / contract and serves as the subject.

So the basic structure is:

• pactum = the agreement
• continet = contains

Summam is accusative singular, which shows that it is the direct object of continet.

The verb continere means to contain, and the thing being contained goes into the accusative case. So:

• summa = sum, amount
• summam = the sum / amount as the direct object

In other words, the agreement contains what?
It contains summam.

Dotis is the genitive singular of dos, dotis, meaning dowry.

The genitive here shows a relationship like of in English:

• summa dotis = the amount of the dowry

So dotis depends on summam and tells us what kind of amount or the amount of what.

Because the sentence is not saying simply the dowry; it is specifically talking about the amount of the dowry.

Compare:

• dotem = the dowry
• summam dotis = the amount of the dowry

Latin often uses this kind of noun + genitive structure to be more precise.

The dictionary form is contineo, continere, continui, contentum.

Continet is:

• 3rd person singular
• present tense
• active voice
• indicative mood

So it means he/she/it contains.
Since pactum is neuter singular, in translation we use it contains.

By itself, pactum could potentially look like the neuter form of the perfect passive participle of paciscor (agreed, having been agreed), but in this sentence it is best understood as a noun meaning agreement or contract.

Why?

Because it fits naturally as the subject of continet, and pactum is also a standard Latin noun meaning agreement.

So here:

• pactum = agreement, contract
  not
• pactum = agreed thing

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

So:

• pactum can mean an agreement or the agreement
• summam can mean a sum, the sum, an amount, or the amount

The exact English article depends on context. In a standalone sentence like this, the meaning has to be supplied by context or by the translator.

Not as much as it would be in English. Latin relies heavily on case endings, so the grammatical roles are already clear:

• pactum = nominative subject
• summam = accusative object
• dotis = genitive dependent on summam
• continet = verb

So even if the order changed, the basic meaning would stay the same. For example, Latin could also say:

• Pactum continet summam dotis
• Summam dotis pactum continet

The original order may give a certain emphasis or flow, but the cases do most of the grammatical work.

A simple breakdown is:

• Pactum — nominative singular neuter; subject; agreement / contract
• summam — accusative singular feminine; direct object; sum / amount
• dotis — genitive singular feminine; dependent on summam; of the dowry
• continet — 3rd person singular present active indicative; contains

So the structure is:

subject + object + verb
= The agreement contains the amount of the dowry.

They are:

• pactum, pacti (neuter) = agreement, contract
• summa, summae (feminine) = sum, amount
• dos, dotis (feminine) = dowry

This is useful because Latin dictionaries list nouns by the nominative and genitive forms, and the genitive helps you identify the declension:

• pacti → 2nd declension
• summae → 1st declension
• dotis → 3rd declension