【Abate】 , 【subside】 , 【wane】 and 【ebb】 all mean to die down in force or intensity.
【Abate】 stresses a progressive diminishing.
【Subside】 suggests a falling to a low level and an easing of turbulence.
【Wane】 adds to 【abate】 an implication of fading or weakening and is often used of something impressive or intense.
【Ebb】 suggests a gradual waning, especially of something that commonly comes and goes.