In water, a cross-current is a flow that runs across the main flow instead of along with it. A river mostly moves downstream, but near a bend, a bridge pillar or a river mouth, some of the water pushes sideways — that sideways push is a cross-current. Swimmers and small boats care about it a great deal, because it moves you off your line without your noticing: you aim at a point on the far bank, you swim straight, and you arrive somewhere else. That is the physical meaning, and it is the one to hold on to. English then borrows the picture for people. When most of a group is moving one way in opinion and a smaller, sideways force is pulling differently underneath, writers call it a cross-current: "there were cross-currents of anger in the meeting", "cross-currents in public opinion". In that use it almost always appears in the plural, and it suggests something felt rather than said out loud — pressures under the surface, exactly as in the river. The word is common in writing about sailing, swimming and news commentary; it is not an everyday spoken word. You will also see it written cross current or crosscurrent; all three spellings appear, and the hyphen is safest.