The crossword solutions for the term 'Tricky Curve' are ESS. This acronym stands for 'Eddy Shear Stress, ' which is a measure of the strength of the turbulent eddies in a fluid flow. It is used to describe the complexity of a curved flow, such as a river bend or an ocean current. The eddy shear stress is an important factor in determining the stability of the flow and the amount of energy it can transfer.