Stinking rich OR Stinkingly rich (See more…)

‘Stinking rich’ is preferred. The idiom is an informal way to describe someone who is very wealthy, often in a way that is perceived as showy or ostentatious. 

For instance:

He is stinking rich after selling his land for millions.

The error in the choice of ‘stinkingly rich’ might stem from the logical extension of adding the suffix ‘-ly’ to ‘stink’ to form an adverb. But it deviates from the conventional idiom.

However, ‘stinking rich’ is an idiomatic expression that uses ‘stinking’ as an intensifier to convey a strong sense of wealth. 

In this context, ‘stinking’ does not literally mean emitting a bad smell, but rather serves to emphasize the extent of one’s wealth.