What is the X in X-mas?
1610s, "wood that has a red hue," from red (adj.1) + wood (n.). Of various types of New World trees that yield such wood, from 1716; specifically of the California Sequoia sempervirens from 1819. In Scottish English 16c.-18c. the same word as an adjective meant "completely deranged, raving, stark mad," from wood (adj.).