La oferto restos ĝis dimanĉo, sed la rabato estos plej granda morgaŭ.

Restos is the future-tense form of resti, which means to remain, to stay, or to continue to be.

Esperanto verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command / wish
• -i = infinitive

So:

• restas = remains
• restis = remained
• restos = will remain

In this sentence, La oferto restos... means the offer will continue to be available.

La is the definite article, like English the.

So:

• la oferto = the offer
• la rabato = the discount

It shows that these are specific things, not just any offer or any discount. Esperanto has only one definite article, la, and it does not change for singular, plural, case, or gender.

Oferto is a noun built from the root ofert-.

In Esperanto:

• -o makes a noun
• -i makes the infinitive form of a verb

So:

• oferti = to offer
• oferto = an offer

This is a very common Esperanto pattern. Once you know a root, you can often build related words very easily.

Ĝis means until or up to.

So:

• ĝis dimanĉo = until Sunday

After a preposition like ĝis, Esperanto normally uses the basic form, not the -n ending. That is why it is dimanĉo, not dimanĉon.

The form dimanĉon can appear in time expressions without a preposition, for example to mean on Sunday, but after ĝis, you normally use dimanĉo.

This can depend a little on context, just like until Sunday in English.

Usually, ĝis dimanĉo means the offer lasts up to Sunday, and many people will understand that Sunday is still part of the time period, or at least that the ending point is on Sunday.

If someone wants to be more precise, they might say something like:

• ĝis la fino de dimanĉo = until the end of Sunday
• ĝis lundo = until Monday

So the sentence is natural, but exact interpretation can depend on context.

In Esperanto, days of the week are normally written with a lowercase letter:

• lundo
• mardo
• merkredo
• ĵaŭdo
• vendredo
• sabato
• dimanĉo

The same is true for months. So lowercase dimanĉo is standard Esperanto spelling.

Granda means big or large.

Esperanto uses:

• pli = more
• plej = most

So:

• granda = big / large
• pli granda = bigger / larger
• plej granda = biggest / largest / greatest

Here, plej granda means the discount will be at its highest or largest level tomorrow.

In Esperanto, just as in English, words for physical size are often used for amount or degree too.

So:

• granda rabato = a large discount

This means a discount of great amount, not physical size. It is completely natural Esperanto.

Because granda is not directly attached to the noun here. It is part of the predicate after estos.

Compare these:

• la plej granda rabato = the biggest discount
• la rabato estos plej granda = the discount will be biggest

In the sentence you gave, rabato is the subject, and plej granda describes it after the verb estos. This is a normal pattern in Esperanto, just like in English with will be biggest or will be the largest.

Morgaŭ is an adverb of time meaning tomorrow.

It does not change form. It is not marked for case, number, or gender.

It tells you when something happens:

• La rabato estos plej granda morgaŭ = the discount will be greatest tomorrow

Yes, it could go somewhere else. Esperanto word order is fairly flexible.

All of these are possible:

• La rabato estos plej granda morgaŭ
• Morgaŭ la rabato estos plej granda
• La rabato morgaŭ estos plej granda

The version in your sentence is a very natural one. Putting morgaŭ at the end gives it a neat final time focus.

Sed means but.

It connects two contrasting ideas:

• La oferto restos ĝis dimanĉo = the offer remains available until Sunday
• sed la rabato estos plej granda morgaŭ = but the discount will be greatest tomorrow

So the contrast is:

• the offer continues for several days
• however, tomorrow is the best day for the biggest discount

Yes. A comma before sed is normal Esperanto punctuation when it links two full clauses.

Here the sentence has two separate parts:

• La oferto restos ĝis dimanĉo
• sed la rabato estos plej granda morgaŭ

So the comma is standard and helps make the structure clear.