Bliss
Etymology
From Old English "bliss" or "blīths", related to "blīthe" (blithe, gentle, kind). Though later associated in feeling with "bless," the two are unrelated in origin; bliss descends from the vocabulary of gentleness and joy, not of holiness.
noun · /bliss/
Perfect, serene happiness.
What it names
Joy in its calmest, most complete form — a fullness so total it is untroubled, unlike the racing high of excitement.
Example
The first hour of the empty house, coffee in hand and no one needing anything, was pure bliss.
Related idea
Bliss is deep, serene contentment; euphoria is an intense, often fragile elation, sometimes chemically induced, that spikes and crashes where bliss simply rests.