1. The cardinal number equal to 3 + 1.
2. The fourth in a set or sequence.
3. Something having four parts, units, or members, such as a musical quartet or a four-cylinder engine.
All four limbs of an animal or person: a baby crawling on all fours.
[Middle English, from Old English fēower; see kwetwer- in the Appendix of Indo-European roots.]
four adj. & pron.
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