Η οφειλή είναι τεράστια.

A natural pronunciation is:

i ofiˈli iˈne teˈrastça

A simpler learner-friendly approximation is:

ee oh-fee-LEE EE-neh teh-RAHS-tya

A few notes:

• Η is pronounced ee.
• οφειλή is stressed on the last syllable: ο-φει-λή
• είναι is stressed on the first syllable: εί-ναι
• τεράστια is stressed on ρά: τε-ρά-στια

Η is the feminine singular nominative form of the definite article, meaning the.

So:

• η οφειλή = the debt

Greek articles change according to:

• gender
• number
• case

Here, η matches οφειλή, which is:

• feminine
• singular
• nominative

In Greek, every noun has a grammatical gender: masculine, feminine, or neuter. Οφειλή is a feminine noun.

Its gender is not about biological sex here; it is just a grammatical property of the word.

You can often recognize feminine nouns by common endings, and -ή is a very common feminine ending. So when learners see οφειλή, they often expect it to be feminine, and that is correct.

Because it is feminine, the article is η and the adjective also has to be in a feminine form: τεράστια.

It is in the nominative case, because it is the subject of the sentence.

In Η οφειλή είναι τεράστια:

• Η οφειλή = the subject
• είναι = the verb is
• τεράστια = describes the subject

So Greek uses the nominative here just as English uses the subject form in The debt is huge.

Greek adjectives must agree with the noun they describe in:

• gender
• number
• case

Since οφειλή is:

• feminine
• singular
• nominative

the adjective must also be:

• feminine
• singular
• nominative

That is why you get τεράστια.

Compare:

• τεράστιος = masculine
• τεράστια = feminine
• τεράστιο = neuter

So:

• η οφειλή είναι τεράστια
• ο λογαριασμός είναι τεράστιος
• το ποσό είναι τεράστιο

Είναι is the present tense form of the verb είμαι, meaning to be.

Here it means is.

A useful thing to know is that είναι is used for:

• he is
• she is
• it is
• and also they are

So Greek does not always distinguish these forms the way English does.

In this sentence:

• Η οφειλή είναι τεράστια = The debt is huge

In standard Modern Greek, usually no. You normally keep είναι in a sentence like this.

So:

• Η οφειλή είναι τεράστια = correct

If you remove είναι, the result does not sound like a normal complete standard sentence.

Greek often allows dropping subject pronouns, but not the main verb to be in this kind of sentence.

Yes. Greek word order is more flexible than English, although the basic version here is very natural:

• Η οφειλή είναι τεράστια.

You may also see:

• Τεράστια είναι η οφειλή.

That version gives more emphasis to τεράστια, roughly like:

• The debt is enormous
• or Enormous is the debt, though that second English version is less natural

So the original sentence is the most neutral and straightforward.

Yes, but that changes the structure.

• Η οφειλή είναι τεράστια = The debt is huge

  • this is a full sentence
  • τεράστια is a predicate adjective after είναι

• η τεράστια οφειλή = the huge debt

  • this is a noun phrase, not a full sentence by itself
  • τεράστια directly modifies the noun

So both are correct, but they do different jobs.

Οφειλή most commonly means debt or financial obligation. Depending on context, it can also refer to money owed more generally.

It is not always exactly the same as bill. A bill might be:

• λογαριασμός in many everyday situations

So οφειλή often sounds a bit more formal or financial:

• an obligation
• an outstanding debt
• an amount due

Context decides the best English translation.

The accent mark shows which syllable is stressed.

So:

• οφειλή → stress on the last syllable
• είναι → stress on the first syllable
• τεράστια → stress on ρά

Stress is important in Greek and should be learned with the word. The accent mark is not optional in normal writing.

No difference in grammar. It is capitalized only because it is the first word of the sentence.

So:

• Η οφειλή είναι τεράστια.
• Βλέπω ότι η οφειλή είναι τεράστια.

Both Η and η are the same word; the capital letter is just normal sentence-initial capitalization.

It is quite neutral and natural, though οφειλή can sound a little more formal than some everyday alternatives depending on context.

So the sentence would fit:

• everyday discussion about money owed
• banking or legal language
• written notices
• general description

It is not especially slangy or highly literary. It is standard Modern Greek.