divide [streams] . (a) The line of separation, or the ridge, summit, or narrow tract of high ground, marking the boundary between two adjacent drainage basins or dividing the surface waters that flow naturally in one direction from those that flow in the opposite direction; the line forming the rim of or enclosing a drainage basin; a line across which no water flows. An "anomalous" divide is one that does not follow the crest of the highest mountain range of a mountain chain. See also: continental divide. British syn: watershed. Syn: drainage divide; height of land; topographic divide; watershed line. (b) A tract of relatively high ground between two streams; a line that follows the summit of an interfluve. (c) The highest summit of a pass or gap. (d) groundwater divide.