Today it means: A watersports discipline, a variant of kayak slalom, where multiple competitors are on-course at the same time, instead of singly, on a whitewater course with downstream and upstream gates, which competitors must pass on the correct side in the correct direction, competing head-to-head, in kayaks. The sport is similar to the wintersports of skicross, snowboardcross, icecross (skating), and the cyclesport of BMX racing. Full definition →
From kayak + cross. From using kayak boats on a cross-country course. Patterned after similar sports such as skicross, snowboardcross, icecross, BMX (“bicycle motocross”), motocross (“MX”), supercross (“SX”).
Etymology from Wiktionary, CC BY-SA 4.0.