serene

Etymology 1

From Middle English, borrowed from Latin serēnus (“clear, cloudless, untroubled”).

adj

1. Calm, peaceful, unruffled.
   She looked at her students with joviality and a serene mentality.
2. Without worry or anxiety; unaffected by disturbance.
3. (archaic) Fair and unclouded (as of the sky); clear; unobscured.
4. Used as part of certain titles, originally to indicate sovereignty or independence.
   Her Serene Highness

verb

1. (transitive) To make serene.

noun

1. (poetic) Serenity; clearness; calmness.
   To their master is denied / To share their sweet serene. 1742, Edward Young, Night Thoughts on Life, Death and Immortality

Etymology 2

Borrowed from Middle French serein, from Old French serein (“evening”), from Vulgar Latin *serānum, from substantive use of sērum, neuter of sērus (“late”) + -ānus suffix.

noun

1. A fine rain from a cloudless sky after sunset.