Merriam-Webster Logo
  • Dictionary
  • Thesaurus
  • Scrabble
  • Spanish Central
  • Learner's Dictionary


noun ter·tia·ry \ˈtər-shē-ˌer-ē, -shə-rē\

Definition of tertiary



  1. 1 [Medieval Latin tertiarius, from Latin, of a third] :  a member of a monastic third order especially of lay people

  2. 2 capitalized :  the Tertiary (see 2tertiary)period or system of rocks

Circa 1550

First Known Use of tertiary

circa 1550

Rhymes with tertiary

actuary, adversary, airy-fairy, ancillary, antiquary, apiary, arbitrary, aviary, axillary, bacillary, beriberi, bestiary, biliary, black raspberry, Bloody Mary, boysenberry, breviary, budgetary, calamari, calamary, candleberry, Canterbury, capillary, carpellary, cassowary, catenary, cautionary, cavitary, cemetery, centenary, certiorari, checkerberry, chinaberry, cometary, commentary, commissary, condottiere, coralberry, corollary, coronary, culinary, customary, dictionary, dietary, dignitary, dromedary, dysentery, elderberry, emissary, estuary, farkleberry, February, formulary, fragmentary, fritillary, functionary, funerary, honorary, huckleberry, intermarry, janissary, January, lamasery, lapidary, lectionary, legendary, legionary, lingonberry, literary, loganberry, luminary, mammillary, mandatary, maxillary, medullary, mercenary, miliary, military, millenary, milliary, millinery, missionary, momentary, monastery, mortuary, necessary, ordinary, ossuary, partridgeberry, pensionary, pigmentary, planetary, Pondicherry, prebendary, presbytery, pulmonary, quaternary, red mulberry, reliquary, rowanberry, salivary, salmonberry, salutary, sanctuary, sanguinary, sanitary, secondary, secretary, sedentary, seminary, silverberry, solitary, sour cherry, stationary, stationery, statuary, subcontrary, sublunary, sugarberry, sumptuary, syllabary, temporary, thimbleberry, Tipperary, Tom and Jerry, topiary, tributary, tutelary, Typhoid Mary, unitary, urinary, vestiary, Virgin Mary, visionary, voluntary, vulnerary, Waterbury, whortleberry, winterberry



adjective ter·tia·ry \ˈtər-shē-ˌer-ē, -shə-rē\

Simple Definition of tertiary

  • : third in order, importance, or value

Source: Merriam-Webster's Learner's Dictionary

Full Definition of tertiary

  1. 1a :  of third rank, importance, or valueb chiefly British :  of, relating to, or being higher educationc :  of, relating to, or constituting the third strongest of the three or four degrees of stress recognized by most linguists (as the stress of the third syllable of basketball team)

  2. 2 capitalized :  of, relating to, or being the first period of the Cenozoic era or the corresponding system of rocks marked by the formation of high mountains (as the Alps, Caucasus, and Himalayas) and the dominance of mammals on land — see geologic time table

  3. 3a :  involving or resulting from the substitution of three atoms or groups <a tertiary salt> <tertiary amine>b :  being or containing a carbon atom having bonds to three other carbon atoms <an acid containing a tertiary carbon> <tertiary alcohols>c :  of, relating to, or being the normal folded structure of the coiled chain of a protein or of DNA or RNA

  4. 4 :  occurring in or being a third stage: asa :  being or relating to the recovery of oil and gas from old wells by means of the underground application of heat and chemicalsb :  being or relating to the purification of wastewater by removal of fine particles, nitrates, and phosphates

Examples of tertiary in a sentence

  1. Bill Clinton … has passed through the tertiary and quaternary stages and is well on his way to millenary integrity. —Cullen Murphy, Atlantic, January/February 2003

  2. A tertiary care doctor at a cushy academic medical center, a plastic surgeon, and a dentist in a Pleasantville suburb don't spend much time taking care of poor patients who lack basic insurance. —Siddhartha Mukherjee, New Republic, 17 Sept. 2001

  3. The most learned philosopher knew little more. He had partially unveiled the face of Nature, but her immortal lineaments were still a wonder and a mystery. He might dissect, anatomise, and give names; but, not to speak of a final cause, causes in their secondary and tertiary grades were utterly unknown to him. —Mary Wollstonecraft Shelley, Frankenstein, 1818

  4. Headaches often occur during the tertiary stage of the illness.

Origin and Etymology of tertiary

Latin tertiarius of or containing a third, from tertius third

First Known Use: circa 1656

Medical Dictionary



play play
noun ter·tia·ry \ˈtər-shē-ˌer-ē, ˈtər-shə-rē\

Medical Definition of tertiary



  1. 1:  tertiary color

  2. 2:  a lesion of tertiary syphilis



adjective ter·tia·ry

Medical Definition of tertiary

  1. 1:  of third rank, importance, or value

  2. 2a:  involving or resulting from the substitution of three atoms or groups <a tertiary salt>b:  being or containing a carbon atom having bonds to three other carbon atoms <an acid containing a tertiary carbon>c:  of, relating to, or being the normal folded structure of the coiled chain of a protein or of a DNA or RNA—compare primary 4, secondary 3

  3. 3:  occurring in or being a third stage <tertiary lesions of syphilis>

  4. 4:  providing tertiary care <a tertiary medical center>

Learn More about tertiary

Seen and Heard

What made you want to look up tertiary? Please tell us where you read or heard it (including the quote, if possible).


a simplified speech bridging languages

Get Word of the Day daily email!


Take a 3-minute break and test your skills!


Which is a synonym of indolent?

melancholy philistine frenetic lazy
Name That Thing

Test your visual vocabulary with our 10-question challenge!


Test Your Knowledge - and learn some interesting things along the way.