Pas ima veliku kost.

Because pas is the subject of the sentence, so it is in the nominative singular.

• pas = nominative singular, used for the subject
• psa = accusative/genitive singular, used in other roles

In Pas ima veliku kost, the dog is the one doing the having, so Croatian uses pas.

Ima is the 3rd person singular present tense of imati, which means to have.

The subject pas is singular, so the verb must also be singular:

• ja imam = I have
• ti imaš = you have
• on/ona/ono ima = he/she/it has

So pas ima means the dog has.

Because veliku is the form of velik that agrees with kost in:

• gender: feminine
• number: singular
• case: accusative

Since kost is the direct object, it is in the accusative. The adjective must match it, so:

• nominative feminine singular: velika
• accusative feminine singular: veliku

That is why you get veliku kost.

It is in the accusative, but for this noun, the nominative singular and accusative singular happen to look the same.

So:

• nominative: kost
• accusative: kost

The case is still there grammatically; it just is not visible on the noun itself. You can see it more clearly on the adjective:

• velika kost = nominative
• veliku kost = accusative

So the adjective shows the case more obviously than the noun does.

• pas is masculine
• kost is feminine

In Croatian, every noun has a grammatical gender. This affects adjectives and some other words that go with the noun.

So in this sentence:

• pas does not force any adjective agreement because it has no adjective here
• kost is feminine, so the adjective must also be feminine: veliku

Croatian normally does not use articles like English a and the.

So Pas ima veliku kost can mean things like:

• The dog has a big bone
• A dog has a big bone
• sometimes even The dog has the big bone, depending on context

Croatian usually leaves this to context. If speakers need to be more specific, they can use words like taj for that or other expressions.

No, Croatian word order is fairly flexible.

Pas ima veliku kost is the most neutral order here:

• Pas = subject
• ima = verb
• veliku kost = object

But other orders are possible if you want different emphasis, for example:

• Veliku kost ima pas. = emphasis on big bone
• Ima veliku kost. = the subject is omitted because it is understood from context

So the version you have is the most straightforward, neutral one.

You can tell from both the noun and the adjective.

• kost = singular
• kosti = plural
• veliku = feminine singular accusative
• plural would be different, for example velike

So:

• veliku kost = one big bone
• velike kosti = big bones

The sentence clearly uses the singular.

A rough English-friendly pronunciation is:

pahs EE-mah VEH-lee-koo kost

A few useful notes:

• a is usually like a in father
• i is like ee in see
• e is like e in bed
• o is like o in more, but shorter and cleaner
• v is like English v
• k, t, p are usually less strongly puffed than in English

So each word is pronounced quite clearly:

• pas
• ima
• veliku
• kost

No. This is grammatical gender, not biological sex.

In Croatian, nouns belong to gender classes such as masculine, feminine, and neuter. That affects grammar, especially adjective endings, but it does not mean the thing itself is male or female.

So kost is feminine only in the grammatical sense.