Odor rosae suavis est.

Because rosae is genitive singular here, meaning of the rose.

Latin often uses the genitive case where English uses of:

• odor rosae = the smell/scent of the rose

The base noun is rosa (rose), a first-declension noun:

• nominative singular: rosa
• genitive singular: rosae

So rosae shows a relationship to odor: it tells us whose smell it is.

Odor is nominative singular because it is the subject of the sentence.

The sentence is built like this:

• odor = the subject
• rosae = a genitive dependent on odor
• suavis = predicate adjective describing the subject
• est = is

So the core structure is:

• Odor ... suavis est = The smell ... is sweet/pleasant

Because suavis belongs to a different adjective pattern.

Not all Latin adjectives use -us, -a, -um.
Suavis, suave is a third-declension adjective:

• masculine/feminine nominative singular: suavis
• neuter nominative singular: suave

Since odor is masculine singular nominative, the correct agreeing form is suavis.

So:

• odor suavis = a sweet/pleasant smell

It agrees with odor, not with rosae.

In Latin, an adjective agrees with the noun it describes in:

• gender
• number
• case

Here suavis describes odor, so it matches odor:

• odor = nominative singular masculine
• suavis = nominative singular masculine/feminine form

It does not describe rosae.
Rosae is genitive singular and depends on odor.

Because Latin word order is much more flexible than English word order.

English depends heavily on position:

• The smell of the rose is sweet

Latin depends more on endings than on word order:

• Odor rosae suavis est

This means Latin can move words around for emphasis or style.
For example, all of these could mean essentially the same thing:

• Odor rosae suavis est
• Rosae odor suavis est
• Suavis est odor rosae

The endings tell you how the words function.

Yes, rosae is a form that can have more than one grammatical value, depending on context.

For a first-declension noun like rosa, rosae can be:

• genitive singular = of the rose
• dative singular = to/for the rose
• nominative plural = roses

But in this sentence, odor rosae clearly means the smell of the rose, so rosae is genitive singular.

This is very common in Latin: one form can have several possible meanings, and context tells you which one is correct.

Because Classical Latin has no definite article and no indefinite article.

So Latin does not normally have separate words for:

• the
• a/an

A noun like odor can mean:

• smell
• a smell
• the smell

The exact sense comes from context.

So Odor rosae suavis est can naturally be understood as:

• The smell of the rose is sweet or
• A rose’s scent is sweet

Not necessarily.

In English, odor can sometimes sound unpleasant, but in Latin odor is more neutral. It can mean:

• smell
• scent
• odor

Because the adjective suavis is positive, the whole phrase clearly has a pleasant sense:

• odor rosae suavis = the sweet/pleasant scent of the rose

So here odor is not negative.

Yes, sometimes.

Latin can omit forms of to be, especially in:

• poetry
• short sayings
• highly compressed style

So you may sometimes see something like:

• odor rosae suavis

with est understood.

But in straightforward prose, est is often included, as it is here:

• Odor rosae suavis est

In a common Classical pronunciation, it would be roughly:

• Odor = OH-dor
• rosae = RO-sigh
• suavis = SWA-wis
• est = est

So approximately:

OH-dor RO-sigh SWA-wis est

A more technical Classical pronunciation would be something like:

/ˈo.dor ˈro.sae̯ ˈswa.wis est/

The most important beginner points are:

• v is pronounced like w
• ae sounds like the ai in aisle