The definition of tranquil is someone or something that is calm and peaceful.
Serenely self-possessed; calm:
free from emotional agitation or nervous tension; ; - Anthony Trollope
The definition of placid is calm or quiet.
(Of water) with little waves on the surface.
Not agitated emotionally; calm:
Find another word for unperturbed. In this page you can discover 15 synonyms, antonyms, idiomatic expressions, and related words for unperturbed, like: tranquil, undisturbed, composed, unflurried, placid, calm, unflustered, unruffled, unfazed, unfaze and unmoved.