The word "油腻" is formed by combining the character "油", which means oil or greasy, with the character "腻", which means greasy or oily. Together, they create a compound word that literally refers to something containing or resembling oil or fat, such as greasy food. This direct combination of two semantically similar characters emphasizes the quality of greasiness, and the word can also be applied metaphorically to describe people or behaviors that are overly slick or unpleasantly smooth.