Medicus os fractum videt.

Because medicus is in the nominative singular, the case normally used for the subject.

• medicus = doctor
• nominative singular ending: -us for this second-declension masculine noun

So medicus is the one doing the action of videt.

Os is the direct object of videt, so it is in the accusative singular.

A useful point: os is a neuter noun, and in Latin, neuter nominative and accusative singular are often identical. So the form os can look the same in both cases.

Here it is understood as accusative because it is the thing being seen.

Because adjectives in Latin must agree with the noun they describe in:

• gender
• number
• case

Here os is:

• neuter
• singular
• accusative

So the adjective must also be neuter singular accusative:

• masculine: fractus
• feminine: fracta
• neuter: fractum

So os fractum means broken bone.

Because the endings do not match medicus.

• medicus is masculine nominative singular
• fractum is neuter accusative singular

That means fractum cannot describe medicus. It matches os instead.

Latin often makes these relationships clear through agreement, not just word order.

Latin has no articles. There is no separate word for the or a/an.

So medicus can mean:

• the doctor
• a doctor

and os fractum can mean:

• the broken bone
• a broken bone

English has to choose an article when translating, but Latin does not express it directly.

Videt is the 3rd person singular present active indicative of vidēre, meaning to see.

So videt means:

• he sees
• she sees
• it sees

Because the subject is medicus, we understand it as the doctor sees.

The verb ending -t tells you it is third person singular.

Latin word order is much more flexible than English word order because Latin uses case endings to show grammatical function.

Putting the verb at the end is very common and often feels natural in Latin:

• Medicus os fractum videt.

But other orders are also possible, for example:

• Medicus videt os fractum.
• Os fractum medicus videt.

These can all mean the same basic thing, though the emphasis may shift slightly.

Yes, it is not a second-declension noun. It belongs to the third declension.

Its dictionary form is:

• os, ossis = bone

So its forms do not follow the -us / -um pattern of second-declension nouns.

For example:

• nominative singular: os
• genitive singular: ossis

That is why the accusative singular here is simply os, not ossum.

Yes. Latin actually has two different nouns spelled os:

• os, ossis = bone
• os, oris = mouth

They are different words with different genitives.

In a sentence by itself, os can be ambiguous. Context or the given meaning tells you which one is intended. In this sentence, the meaning shown to the learner makes it clear which os is meant.

Yes. Latin often leaves out subject pronouns and even subject nouns when the verb ending already makes the person clear.

Since videt already means he/she/it sees, Latin could simply say:

• Os fractum videt.

That would mean something like He/She sees a broken bone, depending on context.

Including medicus makes the subject explicit: the doctor.