Placid means calm and hard to upset. A placid lake, a placid child, a placid old horse. It describes a settled temperament or an untroubled surface.
Applied to people it is warm but faintly damning: placid suggests a person who does not react much, which can read as easy-going or as unexciting depending on who is speaking. It is used a great deal of animals, where it is straightforwardly a compliment — a placid pony is one a beginner can ride. Compare calm, which is the everyday word, serene, which is grander, and phlegmatic, which is the same idea with a note of coldness.
1adjectiveplacidCalm and not easily upset.
“She has a placid temperament and it is a considerable advantage.”
synonyms: serene, even-tempered, unruffled
2adjectivewaterOf water, still and undisturbed.
“The lake was placid all morning.”
placid is a quality of calm.
Also accepted in games: serene
Latin placidus meant pleasing or gentle, from placere, to please — the same verb behind please, pleasant and placate. Something placid is agreeable in the oldest sense: it does not disturb you.
French
placide
English, today
placid
Built from
From French placide. French placide, from Latin placidus (“peaceful, calm, placid”), from placeō (“please, satisfy”).
Etymology from Wiktionary, CC BY-SA