- A group or set of four people or things.<ref name="COED-etym&sense"/>
- (context, mathematics) A four-dimensional hypercomplex number that consists of a real dimension and 3 imaginary ones (i, j, k) that are each a square root of -1. They are commonly used in vector mathematics and three-dimensional games. Quaternion multiplication is the most common technique used by mathematicians to avoid gimbal lock when rotating vectors.<ref name="COED-etym&sense"/>
Etymology: From quaterniounMiddle English, quaternioun, from quaternioLatin, quaterniÅ, from quaterniLatin, quaternÄ (ablative form of quaterLatin, quater, "four times") + -ionLatin, -iÅn, "-ionEnglish, -ion".<ref name="D.C-etym">Dictionary.com Unabridged (v 1Â1)</ref><ref name="AHD-etym">The American HeritageÂ Dictionary of the English Language, Fourth Edition</ref><ref name="COED-etym&sense">The Concise Oxford English Dictionary Eleventh Edition</ref>
- Dutch: quaternion(nl)n
- French: quaternion(fr)m
- Italian: quaternione(it)m
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