adverb taking the 'to' particle, adverb
in large quantities; a lot; big time
Mimetic adverb describing earning, gaining, or obtaining something in large amounts, often money. Used with 儲ける, 稼ぐ, もうける, etc.
I made a killing in stocks.
He's raking it in with his new business.
Mimetic word; the exact origin is uncertain, but it likely derives from the sound-symbolic element がっぽ (gappo) suggesting a large amount or a grabbing motion.