Where It Comes From
Ineffable comes from Latin ineffabilis — in- ("not") plus effabilis ("able to be spoken"), itself from effari, "to utter." The word entered English in the late 1300s almost entirely in religious writing, describing things considered too sacred or too vast for human language to capture — the nature of God, the experience of divine revelation.
Centuries later, the word broadened to cover any experience — sacred or not — that leaves you reaching for words that don't exist.
Say It Around the World
Spanish and French borrowed the word almost unchanged from the same Latin root as English. German went its own way, building a native compound from sagen ("to say") plus un- ("not") — literally "unsayable."
The next word describes something so common, so everywhere, that you'd have a hard time escaping it even if you tried.