बिल्ली पालतू जानवर है।

Hindi usually does not use articles the way English does. So बिल्ली can mean a cat, the cat, or even cats in a general sense, depending on context.

That means this sentence can work as a general statement like A cat is a pet animal or Cats are pet animals.

If you want to make a more explicit, you can say:

बिल्ली एक पालतू जानवर है।

That is also correct.

Not necessarily. बिल्ली is the normal everyday Hindi word for cat, and it is grammatically feminine. In many cases, grammatical gender in Hindi is just part of the noun and does not always mean natural sex is being emphasized.

So in a general sentence like this, बिल्ली can simply mean cat as an animal, not specifically female cat.

पालतू means domesticated, tame, or pet depending on context. In this sentence, it is describing जानवर, so it works like an adjective:

• पालतू जानवर = pet animal / domesticated animal

A useful thing to know is that पालतू usually does not change form for gender or number in normal usage. So you can see it with many different nouns:

• पालतू कुत्ता
• पालतू बिल्ली
• पालतू जानवर

Because पालतू जानवर is a full noun phrase meaning pet animal.

If you say:

बिल्ली पालतू है।

that means something like The cat is tame/domesticated or The cat is a pet, depending on context.

But:

बिल्ली पालतू जानवर है।

is more of a classification statement: A cat is a pet animal.

So adding जानवर makes the meaning more explicit and more like a definition.

Hindi often uses the singular in general statements like this, just as English can say:

• A cat is a pet animal

even though it is really talking about cats as a type.

So जानवर is singular because the sentence is presenting cat as belonging to the class pet animal. This is completely natural.

है is the present-tense form meaning is.

In this kind of simple sentence, the structure is:

subject + description/classification + है

So:

• बिल्ली = subject
• पालतू जानवर = classification
• है = is

In the present tense, है does not change for masculine vs. feminine nouns. For example:

• लड़का अच्छा है।
• लड़की अच्छी है।

The adjective changes there, but है stays the same.

So बिल्ली being feminine does not make है change.

Because पालतू जानवर is the predicate noun phrase, not an adjective that has to agree with बिल्ली in the same way.

The sentence is saying:

A cat is a pet animal

not

A cat is pet-like.

So जानवर stays जानवर because it is its own noun. Hindi does not force a predicate noun to change just to match the subject’s gender.

Also, पालतू usually stays the same anyway.

Yes. That is perfectly correct.

Adding एक makes the sentence feel closer to the English pattern A cat is a pet animal.

Without एक, the sentence still sounds natural and often a little more general or definition-like. So both are fine:

• बिल्ली पालतू जानवर है।
• बिल्ली एक पालतू जानवर है।

The version without एक is very common in simple explanatory sentences.

Because this is a basic present-tense equational sentence, not an action sentence.

There is no direct object here, and no ergative construction. The sentence is simply identifying or classifying something:

बिल्ली = subject
पालतू जानवर = what it is
है = is

So no को, ने, or other postposition is needed.

The normal order here is:

subject + predicate + है

So:

बिल्ली पालतू जानवर है।

is the natural basic order.

If you move things around, the sentence may sound unnatural or the emphasis may change. For example, starting with पालतू जानवर could sound like you are contrasting or redefining something rather than simply stating the fact.

For a learner, the safest pattern is:

X Y है
= X is Y

That mark is called the danda. It functions like a period in Hindi writing.

So:

बिल्ली पालतू जानवर है।

ends the sentence the same way . does in English.