- The cardinal number equal to 3 + 1. (noun)
- The fourth in a set or sequence. (noun)
- Something having four parts, units, or members, such as a musical quartet or a four-cylinder engine. (noun)
- All fours All four limbs of an animal or person: a baby crawling on all fours. (idiom)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.