This is the 11470th most frequent Korean word.
끈끈이
A "끈끈이" is a sticky or adhesive substance, or it can refer to a sticky trap (e.g., for catching insects).
In this sentence, 끈끈이 indicates sticky glue or grime on the skin.
피부에 끈끈이가 묻어서 씻어내야 했어요.
I had to wash off the sticky glue that got on my skin.
끈끈이 describes an adhesive characteristic that causes dirt to stick.
끈끈이가 강해서 쓰레기가 쉽게 떨어지지 않아요.
The sticky adhesive is strong, so the dirt does not come off easily.
Here, 끈끈이 refers to an adhesive or sticky component.