Ĉi-matene mi malfermis la fenestron, ĉar la ĉambro estis tro varma.

Ĉi-matene means this morning.

The part matene means in the morning / morning-time, and ĉi adds the idea of this. In expressions of time like this, Esperanto often uses a hyphen:

• ĉi-matene = this morning
• ĉi-vespere = this evening
• ĉi-nokte = tonight

You may also see other ways to express a similar idea, but ĉi-matene is a very common and natural form.

Malfermis is the past-tense form of the verb malfermi, meaning to open.

It breaks down like this:

• ferm- = close, shut
• mal- = the opposite
• malfermi = to open
• -is = past tense

So:

• mi malfermas = I open / I am opening
• mi malfermis = I opened
• mi malfermos = I will open

A very important Esperanto pattern is mal-, which often creates the opposite meaning of a word.

The -n marks the direct object.

In this sentence, la fenestron is the thing being opened, so it gets -n:

• mi malfermis la fenestron = I opened the window

This is called the accusative ending. Esperanto uses it to show which noun receives the action.

Compare:

• la fenestro = the window
• la fenestron = the window (as direct object)

Because la ĉambro is the subject of the clause la ĉambro estis tro varma.

In that clause:

• la ĉambro = the room
• estis = was
• tro varma = too warm

The room is not receiving an action. It is simply the thing being described, so it stays in the basic noun form -o, not the accusative -on.

Because varma describes the noun ĉambro.

In Esperanto:

• -a = adjective
• -e = adverb

So:

• varma = warm
• varme = warmly / in a warm way

Since the sentence means the room was too warm, you need the adjective varma to describe ĉambro.

This is a very common beginner question.

• tre = very
• tro = too, meaning more than is good/comfortable/necessary

So:

• tre varma = very warm
• tro varma = too warm

In this sentence, tro varma shows that the room was warmer than the speaker wanted, which explains why they opened the window.

Ĉar means because. It introduces the reason for the action.

So the sentence structure is:

• Ĉi-matene mi malfermis la fenestron = This morning I opened the window
• ĉar la ĉambro estis tro varma = because the room was too warm

This is a very straightforward way to connect a result and its cause.

Because both actions or states are being presented as past events.

• malfermis = opened
• estis = was

The speaker is talking about what happened this morning, so both the action and the reason for it are in the past:

• I opened the window
• because the room was too warm

This matches English closely.

La is the definite article, meaning the.

It is used because the speaker is talking about a specific window and a specific room, not just any window or any room. In context, these are probably already understood:

• la fenestron = the window
• la ĉambro = the room

Esperanto has only one definite article: la. It does not change for gender, number, or case.

Yes, Esperanto word order is fairly flexible, especially because endings show the grammatical roles.

For example, the core meaning would still be clear in forms like:

• Mi malfermis la fenestron ĉi-matene, ĉar la ĉambro estis tro varma.
• Ĉar la ĉambro estis tro varma, mi malfermis la fenestron ĉi-matene.

However, the original order is very natural and easy to understand. Beginners should usually stick to straightforward word order like this until they feel comfortable with the grammar.

A rough pronunciation guide is:

chee mah-TEH-neh mee მალ-fehr-MEES lah feh-NEHS-tron, char lah CHAM-bro EH-stees troh VAR-ma

A few helpful reminders:

• ĉ sounds like ch in church
• ŝ would sound like sh (not used here, but useful to know)
• c sounds like ts
• Stress is almost always on the second-to-last syllable

So:

• ĉi-matene → stress on te
• malfermis → stress on fer
• fenestron → stress on nes
• ĉambro → stress on ĉam
• varma → stress on var

Very often, yes. Esperanto likes building opposites with mal-.

Examples:

• fermi = to close

• malfermi = to open

• varma = warm

• malvarma = cold

• granda = big
• malgranda = small

This is one of the language’s most useful patterns. Once you know a word, you can often form its opposite easily with mal-.