Century
The account of a generation... this covers a whole generation, and considering how long Japanese people live, this account totals a whole century.
せいき
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.
「今って何世紀だっけ？」「二十一世紀だよ。」
"What century is it right now?" "It's the 21st century."
コウイチは少なくとも一世紀は生きたいと思っている。
Koichi wants to live at least a century.
あいにく、その日のスケジュールは少しきついですね。今世紀最大の日本語学習祭り関連の会議がいくつか入っているんですよ。
I’m afraid my schedule is a little tight that day. I have several meetings related to a Japanese learning festival, which will be the largest one this century.