What does the "주" in 재주 mean?

I know that 재주 means, "talent" or "ability." (Here is the Naver dictionary definition of 재주.) What I do not know is why the 주 was added to 재(才)?

재(才) and 재주 mean the same thing, so why is the 주 needed? Regardless of what the Naver dictionary may say, the 주 of 재주 has no Chinese character orgin that I know of, and I have found no pure Korean word or suffix that might explain it. It just seems to be acting as a filler.

Was 주 added to distinguish 재(才) from other 재's, such as 재(財), which means "property"? For example, without 주 we would not know if 재가 있는 사람 means "a man of talent" or "a man of property." However, when we talk about "a man of property," we normally say 재산 있는 사람, so we could say 재(才)가 있는 사람 without causing any confusion.

Maybe 재주 was originally a pure Korean word, and someone back in history just decided to spice up the word by replacing the pure Korean 재 with the Chinese character 재(才)?

I am not going to answer my question because I do not know the answer; I just wanted to pose it.

Does anyone know of any other examples of a non-Chinese-character 주 being attached to other Chinese characters?