Very, Much, Greatly, A Lot Of, Very Much
adverb
This words is all about doing something in a big way. Particle に on the end tells us its an adverb, meaning that it describes how an action is carried out. It can mean very, a lot of, or greatly, depending on the context.
おおいに
You learned this reading when you learned 大きい. If you can remember that, you should be able to remember this one too!
大いにまなびましょう。
Let’s learn a lot!
王は王子と王女に、「大いにこくみんのぜいきんをつかっていいぞ」といった。
The king said to the prince and the princess, "Go ahead and use a lot of the citizens' tax money."
きょうは大いにのみたまえ。
Please drink a lot today.