Mi malfermas la leterkeston, ĉar mi atendas leteron.

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Breakdown of Mi malfermas la leterkeston, ĉar mi atendas leteron.

• ĉar: because
• atendi: to wait
• letero: the letter

Questions & Answers about Mi malfermas la leterkeston, ĉar mi atendas leteron.

Why do leterkeston and leteron end in -n?

The -n ending marks the direct object in Esperanto.

In this sentence:

• Mi malfermas la leterkeston = I open the mailbox
  • la leterkeston is the thing being opened, so it gets -n
• mi atendas leteron = I am expecting a letter
  • leteron is the thing being expected, so it also gets -n

This is called the accusative ending.

A useful pattern is:

• mi vidas la hundon = I see the dog
• mi manĝas pomon = I eat an apple

The thing directly affected by the verb usually takes -n.

Why is it la leterkeston, but just leteron without la?

La means the.

So:

• la leterkeston = the mailbox
• leteron = a letter / some letter

Esperanto has:

• la for definite nouns
• no indefinite article for a/an

So English a letter is simply letero or, as a direct object here, leteron.

The speaker is talking about a specific mailbox, so la is used. But they are expecting a letter, not necessarily a specific one already identified, so la is not used.

What is leterkesto made of? Is it a compound word?