1 an oblique stroke (/) used in writing fractions (3/4), to separate other figures and letters, or to denote alternatives (and/or) and ratios (miles/day).
2 (in full solidus curve) a curve in a graph of the temperature and composition of a mixture, below which the substance is entirely solid.
3 hist. a gold coin of the later Roman Empire.
Etymology: ME (in sense 3) f. L: see SOLID
Useful english dictionary. 2012.