Unu este destul.

Unu is the standalone numeral one.

• un is usually used before a masculine noun, like un băiat = a boy / one boy
• unu is used when one stands on its own, without a noun after it

So in Unu este destul, unu means one by itself: One is enough.

Este means is. It is the 3rd person singular form of a fi = to be.

So:

• unu = one
• este = is
• destul = enough

In everyday Romanian, people sometimes drop este in casual speech, especially in short sentences, so you may hear Unu-i destul or even just Unu destul in very informal contexts. But the full standard form is Unu este destul.

Here destul means enough.

It can also mean quite or fairly in other contexts:

• Este destul de bun. = It is quite/fairly good.
• Avem destul. = We have enough.

In Unu este destul, it clearly means enough.

Both can work, but they are slightly different in tone.

• destul = common, natural, everyday enough
• suficient = more formal, closer to sufficient

So:

• Unu este destul. = very natural
• Unu este suficient. = also correct, but a bit more formal or deliberate

A Romanian speaker would very naturally say destul in normal conversation.

Yes, it is correct and understandable. It means One is enough.

That said, in real conversation Romanians might often say:

• Unul e destul.
• Unul ajunge.
• E destul unul. (depending on emphasis)

So Unu este destul is correct, but in everyday speech you may hear slightly different versions more often.

Both forms exist, but they are used a little differently.

• unu = basic standalone numeral one
• unul = the one or a more emphatic/pronoun-like one

In many contexts, Romanian speakers prefer unul when the number stands alone, especially in speech:

• Unul este destul.
• Unu este destul.

Both are understandable, but unul can sound a bit more complete or natural to many speakers. Unu is still correct, especially when focusing on the number itself.

Unu is pronounced approximately OO-noo.

A rough guide:

• u = like oo in boot
• nu = noo

So the whole word is about OO-noo.

A rough pronunciation is:

OO-noo ES-teh de-STOOL

Word by word:

• Unu = OO-noo
• este = ES-teh
• destul = de-STOOL

The stress usually falls like this:

• U-nu
• ES-te
• de-STUL

Romanian often uses a normal subject + verb + complement order here:

• Unu = subject
• este = verb
• destul = complement

So literally it is One is enough.

Romanian word order is fairly flexible, though, and changing it can change emphasis. For example:

• Destul este unu would sound unnatural in most contexts
• Unul e destul is a very natural spoken version

Yes. It depends on context.

For example:

• talking about cakes: Unu este destul. = One is enough.
• talking about helpers: Unu este destul. = One person is enough.

Romanian often leaves the noun unstated when it is clear from context, just like English does with one.

Yes. A very common alternative is:

Unul ajunge.

Here ajunge literally means reaches / suffices, but in this context it means is enough.

So both are good:

• Unu / Unul este destul.
• Unul ajunge.

The second one is especially common in natural speech.