Since the company invested heavily in research, the business has become increasingly prosperous.

prosperous 是形容词，由动词 prosper（繁荣、兴旺）加上形容词后缀 -ous 构成，表示"繁荣的、兴旺的"。 -ous 是常见的形容词后缀，表示"具有...特性的"或"充满...的"。prosperous 字面意思是"具有繁荣特性的"，即"兴旺发达的"。