sereno
masculine noun
night watchman
"El sereno abrió el portal a medianoche."
The night watchman opened the door at midnight.
adjective
1
serene, even-tempered, calm
"Ella es serena incluso en exámenes."
She's calm even during exams.
2
calm, tranquil, peaceful
"El mar está sereno hoy."
The sea is calm today.