The word "trinity" does not occur in the Bible.
When, in early Christian writings and creeds, was the word "trinity" first used in reference to God?
After that first (known) occurrence, what are some of the other key earliest uses of the word "trinity" in reference to God in Christian writings and creeds?
(Please do not respond with general defenses of the doctrine of the Trinity. This is a doctrinal history question specifically about the earliest uses of the word "trinity" in relation to God.)