from Wiktionary, Creative Commons Attribution/Share-Alike License
- abbr. A piece of timber with a cross section of 4 inches square.
- abbr. A four-wheel-drive vehicle with a four-speed transmission.
- abbr. A four-wheel vehicle with four-wheel-drive.
- abbr. By extension, any four-wheel-drive vehicle.
From its dimensions (4 inches by 4 inches) (Wiktionary)
From four-wheel drive and four-speed (Wiktionary)