Vết ẩm đang lan rộng.

Literally, vết means a mark, trace, stain, spot, and ẩm means damp, moist.

So vết ẩm is literally something like a damp mark or a damp patch. In natural English, it often refers to a damp patch on a wall or ceiling.

In Vietnamese, describing words usually come after the noun.

So:

• vết = mark / stain
• ẩm = damp

That gives vết ẩm = damp mark

This is a very common Vietnamese pattern:

• nhà lớn = big house
• áo đỏ = red shirt
• vết ẩm = damp mark

Đang marks an action as in progress. It is often similar to English be + -ing.

So:

• lan rộng = spread / widen
• đang lan rộng = is spreading

In this sentence, đang tells you that the damp patch is currently getting bigger.

Yes, you can say:

Vết ẩm lan rộng.

That is still natural Vietnamese. Without đang, the sentence is less explicitly focused on the ongoing action right now. It can sound more general or more dependent on context.

So the difference is roughly:

• Vết ẩm đang lan rộng. = The damp patch is spreading.
• Vết ẩm lan rộng. = The damp patch spreads / is spreading / has spread, depending on context.

Vietnamese often leaves time and aspect to context unless the speaker wants to make it clear.

It is two words, but they work together as one idea.

• lan = spread
• rộng = wide

Together, lan rộng means to spread out, widen, expand.

So it is not just that the damp exists; it is spreading over a wider area.

You can think of it as:

• lan = the action
• rộng = the result or extent of that action

The structure is:

Vết ẩm + đang + lan rộng

That is:

• Vết ẩm = subject noun phrase
• đang = aspect marker
• lan rộng = verb phrase

So the pattern is:

noun phrase + aspect marker + verb phrase

This is a very common Vietnamese sentence pattern.

Vietnamese does not have articles like a, an, the in the same way English does.

So vết ẩm could mean:

• a damp patch
• the damp patch

The exact English choice depends on context.

If the patch has already been mentioned, English would usually say the damp patch. If it is being introduced for the first time, English might say a damp patch.

Vietnamese often leaves that unspecified unless some other word makes it clear.

A classifier is not required here.

You could hear something like cái vết ẩm này in a fuller phrase, especially if someone is pointing it out very specifically, but in a simple statement, vết ẩm by itself is completely natural.

That is because vết is already a normal noun meaning mark/stain/trace. Vietnamese often does not use a classifier unless it helps with:

• counting
• pointing something out
• emphasis
• a more natural conversational rhythm in certain contexts

So Vết ẩm đang lan rộng is perfectly normal.

Not exactly.

• ẩm = damp, moist
• ướt = wet

So vết ẩm suggests a patch of dampness, often from seepage or moisture in a wall.
If you said vết ướt, it would sound more like a wet mark or a patch that is actively wet.

For a wall or ceiling problem, ẩm is usually the more natural choice if you mean dampness rather than obvious surface wetness.

It is a very natural sentence in situations like:

• noticing moisture damage in a house
• talking about a wall or ceiling leak
• describing a stain caused by water seepage
• discussing repairs or mold risk

For example, someone might say it after seeing a patch on the ceiling get bigger over time.

So it sounds practical and everyday, especially in home-maintenance contexts.

A rough pronunciation guide is:

• vết: starts with a sound close to English v, and ends abruptly with t
• ẩm: has the hỏi tone, with a dip in the voice
• đang: starts with đ, which is like an English d
• lan: fairly simple and level
• rộng: starts with a Vietnamese r sound that varies by accent, and has a heavy falling tone

A few useful notes:

• vết has the sắc tone
• ẩm has the hỏi tone
• đang and lan have the level tone
• rộng has the nặng tone

If you want to sound natural, the biggest things to focus on are:

1. getting the tones reasonably close
2. making vết end clearly with t
3. making rộng short and heavy rather than drawn out

Yes, in natural translation it could.

Even though vết ẩm literally points to a damp mark/patch, English may sometimes translate the idea more loosely as:

• The damp patch is spreading
• The dampness is spreading
• The stain is spreading

The best English version depends on the context. If the speaker is talking about a visible patch on a wall, The damp patch is spreading is usually the clearest choice.