Slier is a term typically used to describe someone who is cunning, deceitful, or sly. Some synonyms for slier include shrewd, cunning, crafty, astute, wily, artful, clever, deceptive, and conniving. These words all describe individuals who are smart and calculating in their approach to achieving their goals, but may do so through immoral or dishonest means. While a sly or "slier" person may be successful in the short term, their actions can often lead to negative consequences down the line. Thus, it is important to be aware of the behavior of those around us, and to choose ethical and honest means in our own actions.