isotherombrose,a.Phys.Geog.|ˌaɪsəʊθəˈrɒmbrəʊs| [f. as isothere + Gr. ὄµβρος rain + -ose.] Applied to a line (on a map, etc.) connecting places at which the ratio of the summer rainfall to the annual rainfall is the same. 1864Webster cites A. K. Johnston.