Found just once in the New Testament (1 Pet. 1:81 Pet. 1:8
English: American Standard Version (1901) - ASV
8 whom not having seen ye love; on whom, though now ye see him not, yet believing, ye rejoice greatly with joy unspeakable and full of glory:
WP-Bible plugin), the Greek adjective “aneklaletos” meant “unspeakable” or “unable to tell fully.”
The unsaved often see Christians as having unhappy and joyless lives; God says those who are truly His people have a joy which is so great it defies words to express it.