Tôi đợi nửa ngày.

Because Vietnamese does not need a preposition like for in this pattern.

In English, you say:

• I waited for half a day.

In Vietnamese, the duration usually comes directly after the verb:

• Tôi đợi nửa ngày.
• literally: I wait half a day

So the basic pattern is:

• Subject + verb + duration

Other examples:

• Tôi học hai tiếng. = I studied for two hours.
• Anh ấy ngủ cả ngày. = He slept all day.

Đợi means to wait or to wait for.

It can be used:

• by itself, when the thing/person being waited for is understood
• with an object, when you want to say who or what you are waiting for

Examples:

• Tôi đợi. = I’m waiting.
• Tôi đợi bạn. = I’m waiting for you.
• Tôi đợi nửa ngày. = I waited / have been waiting for half a day.

So in your sentence, the person or thing being waited for is not stated.

Mostly yes. Đợi and chờ are often interchangeable and both mean wait.

So these are both natural:

• Tôi đợi nửa ngày.
• Tôi chờ nửa ngày.

A learner can usually treat them as near-synonyms. In everyday speech, chờ is often felt to be very common and neutral. Đợi is also common and completely natural.

If you are just starting out, it is enough to know that both are correct here.

Nửa ngày means half a day.

In real use, it is often understood approximately, not always as an exact 12 hours. It can mean:

• about half a day
• a long time, depending on context
• literally half of a day, if the context is precise

If you want to be more exact, Vietnamese often uses hours:

• mười hai tiếng
• 12 giờ

So:

• Tôi đợi nửa ngày. = I waited for half a day.
• Tôi đợi 12 tiếng. = I waited for 12 hours.

Vietnamese often does not mark tense the way English does. Time is usually understood from:

• context
• time words
• aspect markers such as đã, đang, sẽ

So Tôi đợi nửa ngày can mean different things depending on context:

• I waited for half a day
• I’ve been waiting for half a day
• less commonly, in the right context, I will wait half a day

If you want to make the time clearer, you can add markers:

• Tôi đã đợi nửa ngày. = I waited / have waited for half a day.
• Tôi đang đợi nửa ngày rồi. = I’ve been waiting for half a day already.
• Tôi sẽ đợi nửa ngày. = I will wait for half a day.

Not really. In this sentence, nửa ngày is a duration expression, not the thing being waited for.

Compare:

• Tôi đợi bạn. → bạn is the object: the person being waited for.
• Tôi đợi nửa ngày. → nửa ngày tells you how long the waiting lasted.

So the sentence is better understood as:

• Tôi = subject
• đợi = verb
• nửa ngày = duration/time phrase

Usually, Tôi đợi nửa ngày is the more natural way to express duration.

Adding trong is possible in some contexts, but it often changes the feel and may sound less natural for a simple statement of duration.

For basic duration after a verb, Vietnamese commonly uses the direct pattern:

• đợi nửa ngày
• học hai tiếng
• ngủ một lát

So for a learner, Tôi đợi nửa ngày is the safest and most natural choice.

Yes. Both are possible depending on context.

Vietnamese often leaves this kind of distinction open unless something else makes it clear.

For example:

• If you are telling a story about yesterday, it will likely mean I waited half the day.
• If you are complaining right now, it may mean I’ve been waiting for half a day.

If you want to stress the ongoing situation up to now, Vietnamese often adds rồi:

• Tôi đợi nửa ngày rồi. = I’ve been waiting for half a day already.

Nửa ngày is the normal, natural way to say half a day.

Một nửa means one half, but with time expressions, Vietnamese often prefers the shorter form:

• nửa ngày = half a day
• nửa tiếng = half an hour
• nửa năm = half a year

Một nửa ngày is much less natural in an ordinary sentence like this. It might appear in special contexts where you are emphasizing one half of a specific day, but that is not the usual way to express duration.

Yes, that is normal if the listener can understand it from context.

Vietnamese often omits information that is already known or not important.

So these are all possible:

• Tôi đợi. = I’m waiting.
• Tôi đợi bạn. = I’m waiting for you.
• Tôi đợi nửa ngày. = I waited / have been waiting for half a day.
• Tôi đợi bạn nửa ngày. = I waited for you for half a day.

If you want to include both the person and the duration, you can put the object before the duration:

• Tôi đợi anh ấy nửa ngày.

A simple pronunciation guide:

• Tôi: sounds roughly like toy
• đợi: roughly like duh-ee / duh-uy, with a heavy low tone
• nửa: roughly nuh-uh with a dipping-rising tone
• ngày: roughly ngai with a falling tone

The tones are:

• tôi: level tone
• đợi: heavy low tone
• nửa: hỏi tone
• ngày: falling tone

If pronunciation is your focus, the trickiest parts are usually:

• the đ in đợi: this is a Vietnamese d sound, not English z/j/y
• the vowel ư in nửa: this sound does not exist in English
• getting the tones right

Yes, it is natural.

Depending on context, a native speaker might also say:

• Tôi chờ nửa ngày.
• Tôi đã đợi nửa ngày.
• Tôi đợi nửa ngày rồi.

These versions add slightly different feelings:

• Tôi đợi nửa ngày. = plain statement
• Tôi đã đợi nửa ngày. = clearly past/completed
• Tôi đợi nửa ngày rồi. = emphasizes that the waiting has already lasted that long

So your original sentence is correct and natural, especially as a simple example of verb + duration.