Learn Spanish (Latin America): —Llegamos a las ocho. —Entendido.

Entendido is the past participle of the verb entender (to understand). To form the regular past participle for an -er or -ir verb, you drop the ending and add -ido. Here, it's used exactly like the English word "understood" to confirm that you got the message.

Can llegamos also mean "we arrived" in the past tense?

Yes! For -ar verbs like llegar (to arrive), the "we" form is exactly the same in both the present tense (llegamos = we arrive) and the past tense (llegamos = we arrived). You have to use the context of the conversation to know which one is meant.

Why do we need las in a las ocho?

In Spanish, hours are treated as feminine plural nouns because they refer to las horas (the hours). Whenever you say "at" a specific time, you must include las (or la for one o'clock). A las ocho translates literally to "at the eight (hours)".

Is saying just Entendido a normal way to reply to someone?

Yes, absolutely. Just like saying "Understood" or "Got it" in English, replying with the lone past participle Entendido is a very common and natural way to confirm that you comprehend a plan or instruction.