When Was the Word Temerity First Used?

The first known use of temerity was in the 15th century.

When was the word Don't first used?

Don't is the standard contraction for do not. As a contraction for does not, don't first appeared in writing in the latter half of the 17th century, about the same time as the first written appearance of other contracted forms with not, like mayn't and can't.

Is Audacity a synonym for temerity?

Some common synonyms of temerity are audacity, cheek, chutzpah, effrontery, gall, hardihood, and nerve. While all these words mean "conspicuous or flagrant boldness," temerity suggests boldness arising from rashness and contempt of danger.