La unua ĉapitro estis tiel klara, ke eĉ laca leganto povus kompreni ĝin sen vortaro.

La means the, so la unua ĉapitro means the first chapter.

In Esperanto, ordinals like unua often take la when you mean a specific item in a sequence:

• la unua ĉapitro = the first chapter
• la dua paĝo = the second page

Without la, unua ĉapitro would sound more like a first chapter or just first chapter in a more general sense.

Unua is the ordinal form of unu (one).

Esperanto makes ordinals by adding -a to the number root:

• unu = one → unua = first
• du = two → dua = second
• tri = three → tria = third

Because unua is an adjective, it has the adjective ending -a.

Because klara is an adjective, and Esperanto adjectives end in -a.

Here it describes ĉapitro:

• ĉapitro = chapter
• klara = clear

So la unua ĉapitro estis tiel klara means the first chapter was so clear.

If the noun were plural, the adjective would also become plural:

• klaraj ĉapitroj = clear chapters

Tiel ... ke means so ... that.

In this sentence:

• tiel klara = so clear
• ke = that

So:

• estis tiel klara, ke ... = was so clear that ...

This is a very common Esperanto structure:

• Li estis tiel laca, ke li ekdormis. = He was so tired that he fell asleep.
• La tasko estis tiel facila, ke ĉiuj sukcesis. = The task was so easy that everyone succeeded.

Ke introduces a subordinate clause, usually equivalent to English that.

Here it connects the result clause to the main clause:

• La unua ĉapitro estis tiel klara = The first chapter was so clear
• ke eĉ laca leganto povus kompreni ĝin = that even a tired reader could understand it

So ke is doing exactly the job that English that does in so clear that...

Povus is the conditional form of povi (to be able / can). It often means could in the sense of would be able to.

So:

• povus kompreni = could understand / would be able to understand

This fits the idea of a consequence or possibility:

• the chapter was so clear that even a tired reader could understand it

If you said povis kompreni, that would mean was able to understand, which sounds more like a statement about an actual past event. Povus gives a more general or hypothetical sense: any tired reader would be able to understand it.

Because it means a tired reader or even a tired reader, not a specific known reader.

Compare:

• la laca leganto = the tired reader
• laca leganto = a tired reader / any tired reader

Here the sentence is making a general claim about clarity, so the indefinite sense is natural:

• eĉ laca leganto = even a tired reader

Eĉ means even.

It adds emphasis:

• eĉ laca leganto = even a tired reader

The idea is that a tired reader might normally have more difficulty understanding a text, so saying even such a reader could understand it shows just how clear the chapter was.

Because ĝin is the accusative form, used for a direct object.

Here, ĝin refers back to la unua ĉapitro:

• kompreni ĝin = understand it

In Esperanto:

• ĝi = it
• ĝin = it, as a direct object

Since the reader is understanding it, the pronoun must take -n.

Sen means without, so:

• sen vortaro = without a dictionary

There is no accusative -n because sen is a preposition, and prepositions normally take their complement without -n.

So:

• kun libro = with a book
• sen vortaro = without a dictionary
• por infano = for a child

Also, there is no la here because the meaning is general: without a dictionary, not without the dictionary.

Vortaro is built from:

• vort- = word
• -ar- = a collection or group
• -o = noun ending

So vortaro literally means a collection of words, which is why it means dictionary.

This is a useful Esperanto pattern:

• arbaro = forest, from arb-
  • -ar- = a collection of trees
• vortaro = dictionary, a collection of words

That is the normal, clear Esperanto word order:

• eĉ laca leganto = subject
• povus kompreni = verb phrase
• ĝin = object

Esperanto word order is fairly flexible because endings show grammatical roles, but the usual order is still subject–verb–object.

So this part works like:

• [even a tired reader] [could understand] [it]

You could sometimes move words for emphasis, but the version in the sentence is the most straightforward.

Because ke introduces a subordinate clause, and Esperanto normally separates that clause with a comma.

So the sentence is divided like this:

• La unua ĉapitro estis tiel klara,
• ke eĉ laca leganto povus kompreni ĝin sen vortaro.

This is standard punctuation in Esperanto and helps show the structure clearly.