1. Adverb (fukushi)

   more and more; all the more; increasingly

   Usually written using kana alone

   いよいよ薄暮、もうすぐ宵闇。

2. at last; finally; beyond doubt

   Usually written using kana alone

3. (at the) last moment; worst possible time

   Usually written using kana alone

Also written 愈々【いよいよ】iyoiyo、弥々【いよいよ】iyoiyo