plural noun Ecclesiastical.
- noting or containing a carbon atom united to three other carbon atoms.
- formed by replacement of three atoms or groups.
noun, plural ter·ti·ar·ies.
Origin of tertiary
- (of an organic compound) having a functional group attached to a carbon atom that is attached to three other groups
- (of an amine) having three organic groups attached to a nitrogen atom
- (of a salt) derived from a tribasic acid by replacement of all its acidic hydrogen atoms with metal atoms or electropositive groups
noun plural -tiaries
Word Origin for tertiary
1650s, "of the third order, rank, degree, etc.," from Latin tertiarius "of or pertaining to a third," from tertius "third, a third," from root of tres "three" (see three). The geological sense (with capital T-) of "era after the Mesozoic" (which formerly was called the Secondary) is attested from 1794, after Italian terziari, used in this sense 1760 by Italian geologist Giovanni Arduino (1714-1795).
- Relating to or having a carbon atom that is attached to three other carbon atoms in a molecule.
- Relating to an organic molecule, such as an alcohol, in which the functional group is attached to a tertiary carbon.