MacTutor History of Mathematics archive: Math history, by person and by topic

Euclid's Elements, interactive: The original math book, in English, with commentary

Earliest uses of various mathematical symbols: When was that symbol first used, and by whom?

Earliest known uses of some of the words of mathematics: When was that word first used, and by whom?

Math words, and some other words, of interest: Where did that word come from?