serener

adjective
  1. 1

    Peaceful, calm, unruffled.

    โ€œShe looked at her students with joviality and a serene mentality.โ€

  2. 2

    Without worry or anxiety; unaffected by disturbance.

  3. 3

    Fair and unclouded (as of the sky); clear; unobscured.

  4. 4

    Used as part of certain titles, originally to indicate sovereignty or independence.

    โ€œHer Serene Highnessโ€

Source: https://en.wiktionary.org/wiki/serene, https://en.wiktionary.org/wiki/serener