tertiary Definition

tertiary
adj

1. Third in order, degree, importance, etc.
2. Said of education: coming after secondary, eg university or college. Compare primary, secondary.
3. chem.
denoting complete replacement of hydrogen atoms in an organic molecule by other chemical groups. Compare primary, secondary.
4. chem.
denoting extraction of petroleum by high-pressure pumping into rock structures.
5. geol.
Relating to the first period of the Cenozoic era.
Form: Tertiary
6. Relating to rocks formed during this period. See also primary, secondary.

noun tertiaries

1. The first geological period of the Cenozoic era.

Form: the Tertiary
2. RC Church.
A lay person who is affiliated to a monastic order and who follows a slightly modified form of that order's rule.

Etymology: 17c: from Latin tertiarius, from tertius third.