placid
adj.adj. calm and peaceful, without much movement or strong emotion. You use this to describe a person who does not get angry easily or a lake that is very still.
adj. not easily upset or excited; showing a calm and steady temperament. When describing bodies of water or landscapes, it indicates a lack of disturbance or turbulence.
The lake was placid and reflected the trees perfectly.
Despite the chaos of the busy office, she maintained a placid expression and finished her work on time.
The valley was home to a placid community of farmers whose lives remained largely untouched by the political upheavals occurring in the distant capital.
From French placide, from Latin placidus (“peaceful, calm, placid”), from placeō (“please, satisfy”).
Often used predicatively after linking verbs like 'remain' or 'seem'.