जूस ठंडा है।

Because जूस is generally treated as a masculine singular noun in Hindi. Adjectives like ठंडा change to match the gender and number of the noun they describe.

• masculine singular: ठंडा
• feminine singular: ठंडी
• masculine plural: ठंडे

So:

• जूस ठंडा है। = The juice is cold.
• चाय ठंडी है। = The tea is cold.

A simple learner-friendly pronunciation is:

joos than-daa hai

A few details:

• जूस sounds like juice, very close to the English word.
• ठ is a strong aspirated t-like sound. It is not the same as English th in think or this.
• ंड in ठंडा gives a nasal sound before ड.
• है is usually pronounced roughly like hai rhyming with eye.

So the whole sentence is approximately:

joos than-daa hai

है is the present-tense form of to be for he/she/it/this/that and singular nouns.

In this sentence, it works like is in English:

• जूस ठंडा है। = Juice is cold.

Some related forms:

• है = is
• हूँ = am
• हो = are
• हैं = are / is (formal or plural)

Hindi usually puts the descriptive word before है in sentences like this.

So the normal pattern is:

noun + adjective + है

Examples:

• पानी ठंडा है।
• कमरा बड़ा है।
• दूध गरम है।

You may sometimes hear different word orders for emphasis in speech or poetry, but जूस ठंडा है is the standard, natural order.

Hindi usually does not use articles like English a, an, and the.

So जूस ठंडा है can mean:

• The juice is cold
• Juice is cold
• A juice is cold

The exact meaning depends on context. In most everyday situations, the listener understands which one is meant.

It is a borrowed word, coming from English juice, but it is commonly used in Hindi.

Hindi uses many everyday loanwords, especially for food, technology, and modern life. Even when a word is borrowed, Hindi still treats it like a Hindi noun for grammar purposes. That is why it can take masculine agreement here:

• जूस ठंडा है।

In standard Hindi, you normally keep है in a full sentence like this.

• Standard: जूस ठंडा है।

If you say only जूस ठंडा, it may sound incomplete, very casual, or like a label/note rather than a normal sentence.

In conversation, native speakers sometimes drop words informally, but as a learner, it is best to use है.

Yes, but that means something slightly different in structure.

• ठंडा जूस = cold juice
  This is a noun phrase, not a complete sentence.
• जूस ठंडा है। = The juice is cold.
  This is a complete sentence.

So:

• मुझे ठंडा जूस चाहिए। = I want cold juice.
• जूस ठंडा है। = The juice is cold.

Its basic meaning is cold, especially for temperature. In this sentence, it clearly means the juice is cold in temperature.

Depending on context, words from ठंड- can also relate to coolness more generally, but for beginners, the main idea is:

• ठंडा = cold
• गरम / गर्म = hot/warm

Examples:

• पानी ठंडा है। = The water is cold.
• खाना गरम है। = The food is hot.

The adjective and sometimes the verb form would change to match.

If the noun is feminine singular

• चाय ठंडी है। = The tea is cold.

If the noun is masculine plural

• आम ठंडे हैं। = The mangoes are cold.

If the noun is feminine plural

• बोतलें ठंडी हैं। = The bottles are cold.

So this sentence is a good example of an important Hindi pattern:

noun + agreeing adjective + form of होना

Yes, a couple of useful things:

• ठ is a separate consonant, different from त and थ.
• The dot in ं is called anusvāra. Here it helps show the nasal sound in ठंडा.
• ा at the end gives the -aa sound, which is why it is ठंडा, not just ठंड.

So learners often recognize the word as built from:

• ठंड = coldness / cold
• ठंडा = cold

That final ा is what gives the masculine adjective form.