Một giây là đủ.

Word by word:

• một = one
• giây = second
• là = is / to be
• đủ = enough, sufficient

So the sentence is literally One second is enough.

The structure is:

• Một giây = the amount of time being talked about
• là đủ = is enough

So it works like:

• [amount/time] + là đủ
• One second + is enough

This is a very common way to say that some amount is sufficient.

Là is the linking word, similar to is in English.

In Vietnamese, adjectives often do not need là:

• Cái này đủ rồi = This is enough already.

But in patterns like X là đủ where you are identifying some amount or thing as sufficient, là is very natural:

• Một người là đủ = One person is enough.
• Ba phút là đủ = Three minutes is enough.

So in Một giây là đủ, là helps form the idea one second is enough in a neat, complete way.

Sometimes in very informal or context-heavy speech, Vietnamese can drop words, but Một giây là đủ is the more standard and natural full sentence.

Một giây đủ may sound incomplete or less smooth to many learners' ears. If you are learning, use:

• Một giây là đủ.

That is the safest choice.

Because giây is already a unit of measurement: second.

Time units such as these usually do not need an extra classifier in this kind of sentence:

• một giây = one second
• một phút = one minute
• một giờ = one hour

So một giây is completely normal by itself.

In this sentence, đủ is best understood as enough / sufficient, so it behaves like an adjective-like predicate.

Examples:

• Tiền này đủ. = This money is enough.
• Một ngày là đủ. = One day is enough.

Vietnamese does not always divide words into parts of speech in exactly the same way English does, but for a learner, thinking of đủ here as enough / sufficient is very helpful.

It can be literal, but depending on context it can also feel a bit flexible or dramatic.

For example:

• literally: One second is enough
• figuratively: Just one second is enough
• dramatically: A second is all it takes

So the exact nuance depends on the situation.

Not exactly.

Một giây là đủ means One second is enough.

If you want to say Just a second! as in Wait a second!, Vietnamese usually uses other expressions, such as:

• Một giây thôi. = Just a second.
• Chờ một giây. = Wait a second.
• Đợi một chút. = Wait a bit.

So Một giây là đủ is about sufficiency, not usually a request for someone to wait.

Not really. Vietnamese often does not use a dummy subject like English it.

English says:

• It is enough

But Vietnamese can simply say:

• Đủ rồi = Enough already

And in your sentence, the thing being evaluated is stated directly:

• Một giây = one second
• là đủ = is enough

So Vietnamese does not need an extra it here.

A rough guide:

• một — low, heavy tone on ộ; the final t is unreleased
• giây — level tone
• là — falling tone
• đủ — dipping/questioning tone

Tone pattern:

• một = nặng
• giây = ngang
• là = huyền
• đủ = hỏi

If you are practicing carefully, pay special attention to:

• một: short and clipped at the end
• đủ: the hỏi tone

Yes, depending on the nuance.

• Một giây là đủ rồi. = One second is enough already.
• Một giây thôi là đủ. = Just one second is enough.

These add a slightly more natural spoken feel in some contexts.

• thôi often adds the sense of just / only
• rồi can add the sense of already / that’s enough now

It can be used when someone wants to say that a very short amount of time is sufficient.

For example:

• in a dramatic statement: Một giây là đủ để thay đổi mọi thứ.
  = One second is enough to change everything.

• in a practical context: Để kiểm tra cái này, một giây là đủ.
  = One second is enough to check this.

So the sentence can sound neutral, emphatic, or dramatic depending on context.