means A short narrow board mounted on four wheels, ridden by standing on it and pushing off the ground, used for transport, tricks, and general gravity-defiance.

from A plain compound: "skate" plus "board." The "skate" comes from roller skating — which itself borrows from "ice skate," traced back through Dutch "schaats" to an Old French word for stilt or leg-support, a cousin of Latin "scabellum," a little stool. The thing itself grew up in mid-20th-century California, when surfers wanting waves on dry days bolted roller-skate wheels onto planks — early ones were literally called "sidewalk surfboards" before the word "skateboard" rolled in and stuck.