Before Christ
Bc, Bce, Before Common Era
Remember how 紀元後 is "After death" or "AD"? Well, this is the opposite because it has a before (前) in it. It's BC or Before Christ.
きげんぜん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. It will also help if you know how to read 紀元後 already, because then you'll just have to remember the 前.
きょうりゅうがいたのは、紀元前何年ごろまでですか。
Until about what year before Christ did the dinosaurs exist?
今日のコウイチは、自分は紀元前の古代ローマからタイムスリップしてきた男だって言いはってきかないんです。
This Kochi keeps insisting that he's a man who time traveled from pre-Christian, Ancient Rome.
もしタイムマシーンがあったなら、紀元前三千年紀に行ってみたいな。
If time machines existed, I would want to go to 3000 B.C.