A sly smile is a facial expression that conveys a mischievous or playful attitude. It is often characterized by a slight upturn of the corners of the mouth and a twinkle in the eyes. The crossword solutions for the term sly smile are GRIN (4 letters), SMIRK (5 letters), LEER (4 letters), and SNEER (5 letters). A GRIN is a broad, toothy smile that expresses joy or amusement. A SMIRK is a half-smile that is often used to express smugness or superiority. A LEER is a lopsided smile that is often used to express lust or mockery. Finally, a SNEER is a contemptuous facial expression that is characterized by a curled lip.