Smooth (out) is a term used to describe the process of making something EVEN and flat. The crossword solutions for this term are IRON (4 letters), EVEN (4 letters), and PLANE (5 letters). IRON is a tool used to press clothes and other fabrics, while EVEN is an adjective meaning level or uniform. PLANE is a tool used to flatten surfaces. Together, these three words can be used to describe the process of smoothing out a surface.