Again
Once Again
adverb
This is the adverb version of 再, so it shares the meaning again and also has the meaning once again.
Note that this word is somewhat formal and literary.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: Once again, you put a footer in your note because you can't remember the reading to this word because the mnemonic is so bad (sorry!).
男はよろめきながらも、再びゆっくりと歩き始めた。
The man, though staggering, began to slowly walk once again.
この地を再び訪れることになるとは思ってもいなかったよ。
I didn't think I would end up visiting this place again.
次の朝、怪物は再び現れた。
The next morning, the monster appeared again.