Nucile și crustaceele sunt separate.

They are:

• nucile ← nuci = nuts
  Singular: nucă = a nut
• crustaceele ← crustacee = crustaceans / shellfish
  Singular: crustaceu = a crustacean

So in this sentence, both nouns are plural.

Because Romanian usually puts the definite article at the end of the noun instead of using a separate word like English the.

So:

• nuci = nuts
• nucile = the nuts

and

• crustacee = crustaceans
• crustaceele = the crustaceans

This is one of the most important differences from English.

Because the plural form is already crustacee, and then Romanian adds the definite article -le:

• crustacee
  • -le → crustaceele

So the spelling is completely regular. It just looks unusual if you are used to English spelling patterns.

Romanian often uses the definite plural where English might use a bare plural.

So Romanian often says things like:

• Pisicile sunt independente. = Cats are independent.
• Merele sunt scumpe. = Apples are expensive.

In a sentence like Nucile și crustaceele sunt separate, the definite forms sound very natural, especially if you are talking about categories of food on a label, in a kitchen, or in an allergy-related context.

Using nuci și crustacee is possible in some contexts, but nucile și crustaceele sounds more standard and natural here.

Și means and.

It is pronounced like English she, but shorter.

A useful spelling tip:

• ș = the sh sound

So și is not pronounced like English see. It is pronounced shi.

Sunt is the present tense, 3rd person plural form of a fi = to be.

So:

• este = is
• sunt = are

Because the subject is plural — nucile și crustaceele — Romanian uses sunt:

• Nucile și crustaceele sunt separate.
• The nuts and shellfish are separate.

Because separate is the form that agrees with a feminine plural subject.

Here is the key point:

• nuci is a feminine noun
• crustaceu is a neuter noun, but in the plural, neuter nouns behave like feminine

So the adjective must be feminine plural:

• masculine singular: separat
• feminine singular: separată
• masculine plural: separați
• feminine/neuter plural: separate

That is why separate is correct here.

In this sentence, it works like an adjective meaning separate / kept separate.

Romanian often uses forms like this after a fi in the same way English does:

• Ușa este închisă. = The door is closed.
• Produsele sunt separate. = The products are separate.

So even if the form historically comes from a participle, for a learner it is best to understand it here as a normal predicate adjective.

Yes. Nucile și crustaceele sunt separate has a very normal Romanian word order:

• subject: Nucile și crustaceele
• verb: sunt
• adjective/complement: separate

This is the neutral, standard way to say it.

You can change word order in Romanian for emphasis, but this version is the most natural in ordinary use.

A rough English-friendly guide is:

NOO-chee-leh shi kroos-tah-CHEH-eh-leh sunt seh-pah-RAH-teh

A few notes:

• ci in nuci sounds like chee
• și sounds like shi
• ce in crustaceele sounds like che
• sunt is often pronounced closer to sînt in actual speech, even though it is usually written sunt

So the rhythm is fairly smooth, with the stress especially noticeable in crustaceele and separate.