From the Latin quaternārius (“containing or consisting of four”), from quaternī (“four each”, “four at a time”) + -ārius (whence the English suffix -ary); compare the French quaternaire.
- (proscribed) Of fourth rank or order.
- Of a mathematical expression containing e.g. x4.
The etymologically correct fourth ordinal from Latin (following tertiary) is quartary, but quaternary (from the distributive number instead) is common, particularly in biology.
of mathematical expressions