Learn Hardcore Esperanto: Dimanĉo estas mia plej trankvila tago.

In Esperanto, names of the days of the week are usually treated like general nouns for “Monday, Tuesday, …” etc., and when you speak about them in a general sense, you normally don’t use la:

Dimanĉo estas mia plej trankvila tago. – Sunday is my calmest day (in general).
Lundo estas labortago. – Monday is a workday.

You would add la only if you mean a specific Sunday:

La dimanĉo post Kristnasko estis tre trankvila. – The Sunday after Christmas was very calm.

Here, we’re talking about “Sunday” in general, so no article is needed.

Why is Dimanĉo capitalized?

It’s capitalized here mainly because it is the first word of the sentence.

In modern Esperanto usage, names of the days of the week are usually written with a lowercase letter when they appear in the middle of a sentence:

Mi laboras lunde. – I work on Monday(s).
Dimanĉo estas mia plej trankvila tago. – At the beginning of a sentence, it’s capitalized anyway.

So you’ll mostly see lundo, mardo, merkredo, … in the middle of sentences, and capitalized only at sentence start or in titles.

What does the -o ending in Dimanĉo and tago mean?

In Esperanto, the ending -o marks a noun.

Dimanĉo = Sunday (a thing/concept → noun)
tago = day (also a noun)

So any word ending in -o is a noun: hundo (dog), domo (house), amiko (friend), etc. In this sentence, Dimanĉo and tago are both nouns.

What does the -a ending in trankvila mean?

The ending -a marks an adjective in Esperanto.

trankvila = calm, quiet (describing something)
mia plej trankvila tago = my calmest day

Other examples:

bela domo – a beautiful house
granda hundo – a big dog

So trankvila is an adjective modifying the noun tago.

Why is it mia plej trankvila tago and not mio plej trankvilo tago or something like that?

Esperanto doesn’t change the endings on mia the way many European languages change possessive adjectives. The pattern is:

mi (I) → mia (my)
vi (you) → via (your)
li (he) → lia (his)
ŝi (she) → ŝia (her)
ni (we) → nia (our)
ili (they) → ilia (their)
ĝi (it) → ĝia (its)

So:

mia tago – my day
mia trankvila tago – my calm day
mia plej trankvila tago – my calmest day

Only the very last word of the noun phrase (tago) has the noun ending -o. Everything describing it (possessive, adjectives) ends in -a or stays unchanged (like plej).

What is the role of estas in this sentence?

estas is the verb esti (to be) in the present tense: estas = am / is / are.

Esperanto always uses a verb in sentences like “X is Y”; you can’t just put two nouns together as in some languages.

Dimanĉo estas mia plej trankvila tago. – Sunday is my calmest day.
La vetero estas varma. – The weather is warm.
Li estas instruisto. – He is a teacher.

So estas is the “link” between Dimanĉo and mia plej trankvila tago.

Why is tago not tagon? When do I use the -n ending?

The ending -n marks the accusative case (direct object, and also used for some movement expressions). In sentences with esti (to be), there is no direct object, so no -n is used on the nouns:

Dimanĉo estas mia plej trankvila tago. – Both Dimanĉo and tago stay in the basic form (no -n).

Compare:

Mi legas libron. – I am reading a book. (libron gets -n because it’s the direct object.)
La libro estas interesa. – The book is interesting. (No -n because estas doesn’t take a direct object.)

Here, Dimanĉo and mia plej trankvila tago are both “things on either side of estas”, so they stay nominative (no -n).

What exactly does trankvila mean, and how is it different from words like kvieta or paca?

trankvila generally means calm, peaceful, not stressful and can apply to:

people: Li estas trankvila. – He is calm.
situations/days: Trankvila tago. – A calm day.
feelings: Mi sentas min trankvila. – I feel calm.

Related words:

kvieta – quiet, not noisy (focus on low noise level)
paca – peaceful in the sense of “without conflict/war” (paca mondo – a peaceful world)

In mia plej trankvila tago, the idea is “the day when I am least stressed / most at ease,” not just “least noisy.”

How does plej trankvila work? What is the difference between pli and plej?

Esperanto uses pli and plej for comparisons:

pli trankvila – calmer / more calm (comparative)
plej trankvila – calmest / most calm (superlative)

Examples:

Mardo estas pli trankvila ol lundo. – Tuesday is calmer than Monday.
Dimanĉo estas mia plej trankvila tago. – Sunday is my calmest day.

So plej trankvila = “calmest,” and plej is the superlative marker.

Should there be a la in mia plej trankvila tago? Why not mia la plej trankvila tago?

In Esperanto, when you use a possessive like mia, lia, nia, etc., you usually do not add la before the superlative:

mia plej bona amiko – my best friend
lia plej ŝatata libro – his favorite book
mia plej trankvila tago – my calmest day

You can say la plej trankvila tago if there is no possessive:

La plej trankvila tago por mi estas dimanĉo. – The calmest day for me is Sunday.

But “mia la plej trankvila tago” is not normal Esperanto; the possessive mia already makes the phrase definite, so la is usually omitted in that pattern.

Can I change the word order, for example Mia plej trankvila tago estas dimanĉo?

Yes. Esperanto word order is quite flexible, especially with esti (to be). Both are correct and natural:

Dimanĉo estas mia plej trankvila tago.
Mia plej trankvila tago estas dimanĉo.

The meaning is the same; you just emphasize different things slightly:

First version emphasizes Dimanĉo (Sunday).
Second version emphasizes mia plej trankvila tago (your calmest day).

The grammar (endings) stays the same regardless of order.

How would I say “On Sundays, it is my calmest day” or “Sundays are my calmest days”?

There are a couple of natural ways:

Talking about Sundays in general as a repeated time:
- Dimanĉe estas mia plej trankvila tago.
  Literally: “On Sunday(s), it is my calmest day.”
  Here dimanĉe = on Sundays / on Sunday in general.
Pluralizing “days”:
- Dimanĉoj estas miaj plej trankvilaj tagoj.
  “Sundays are my calmest days.”

The original sentence Dimanĉo estas mia plej trankvila tago usually means “Sunday (as a kind of day) is my calmest day,” a general statement comparing it to the other days of the week.

How do you pronounce Dimanĉo and trankvila?

Esperanto pronunciation is regular; every letter has one sound, and stress is always on the second-to-last syllable.

Dimanĉo → di-MAN-ĉo
- di like “dee”
- man like “mahn”
- ĉ like English ch in church
- stress on MAN
trankvila → tran-KVI-la
- tran like “trahn” (with a rolled or tapped r)
- kvi like “kvee” (k + v + ee)
- la like “lah”
- stress on KVI

So the whole sentence sounds roughly like:
di-MAN-ĉo ES-tas MI-a PLEJ tran-KVI-la TA-go (each word stressed on its second-to-last syllable).