How to Say "lookout" in Spanish
The Spanish word for “lookout” is “centinela” — B2 level.

Examples
El centinela se mantuvo alerta toda la noche.
The sentry remained alert all night long.
Pusieron a una centinela en la puerta principal del palacio.
They placed a guard at the main door of the palace.
Los viejos robles parecen centinelas del bosque.
The old oaks look like sentinels of the forest.
One word for both genders
The word 'centinela' always ends in 'a' regardless of whether the person is a man or a woman. You only change the 'el' or 'la' in front.
Describing the person vs. the job
When you use 'el centinela', you are usually talking about the specific person. If you talk about the act of guarding, you might use 'la guardia'.
Avoiding 'Centinelo'
Mistake: “El centinelo está cansado.”
Correction: El centinela está cansado. Even though the guard is a man, the word never changes its ending to 'o'.
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