QUATERNITY
four, IV, tetrad, quatern, quaternion, quaternary, quaternity, quartet, quadruplet, foursome, Little Joe
(noun) the cardinal number that is the sum of three and one
Source: WordNet® 3.1
Etymology
Noun
quaternity (countable and uncountable, plural quaternities)
(countable) A group or set of four.
(uncountable) The state of being four.
Synonyms
• (a group of four): quartet, tetrad; see also quartet
• (state of being four): fourness; see also fourness
Source: Wiktionary
Qua*ter"ni*ty, n. Etym: [LL.quaternitas, fr. L. quaterni four each:
cf. F. quaternité.]
1. The number four. [Obs.] Sir T. Browne.
2. The union of four in one, as of four persons; -- analogous to the
theological term trinity.
Source: Webster’s Unabridged Dictionary 1913 Edition