Definition of trinomial in US English:



  • 1(of an algebraic expression) consisting of three terms.

    • ‘We use the likelihood ratio test on the trinomial probability of the number of nucleotide substitutions over codon positions under the two models and under observed sequence evolution.’
    • ‘In 1881 Gyula Farkas published a paper on Farkas Bolyai's iterative solution to the trinomial equation, making a careful study of the convergence of the algorithm.’
    • ‘We show that the unconditional means derived in this paper are actually the positions of the central nodes in HW's trinomial tree.’
    • ‘There are many other forgeries in the paper to do with primes, Catalan numbers, binomial and trinomial numbers, mixing some genuine examples with the forgeries.’
  • 2Biology
    (of a systematic name for a taxon) consisting of three terms of which the first is the name of the genus, the second that of the species, and the third that of the subspecies or variety.

    • ‘A more recent estimate puts the total number of species at 436 ‘species’ (352 Demospongiae, 49 Calcarea, 35 Hexactinellida) if trinomial taxa, subspecies and varieties are included (R. W. M. van Soest, unpublished data).’
    • ‘The species were initially described as races by Forsman, but were elevated to species level by Bocquet, who considered them as members of the superspecies J. marina and gave them trinomial names.’
    • ‘The trinomial naming system has been abandoned in favor of the usual binomial naming convention.’


  • 1An algebraic expression of three terms.

    • ‘Al-Khwarizmi's concept of algebra can now be grasped with greater precision: it concerns the theory of linear and quadratic equations with a single unknown, and the elementary arithmetic of relative binomials and trinomials.…’
    • ‘In general, you will be trying to factor quadratic trinomials that look like a * y ^ 2 + b * y + c where a, b, and c are expressions not involving y…’
    • ‘A trinomial is the sum of three monomials.’
    • ‘This lesson explains how to factor trinomials.’
  • 2Biology
    A trinomial taxonomic name.

    • ‘Chronomorphs are recognized by a trinomial preceded by a ‘slash’ mark, such as in Ondatra zibethicus Imeadensis.’
    • ‘Elsewhere in this issue, Loomis argues that the use of trinomials should be discontinued, causing Witmer Stone to write a letter stating that saving trinomials was ‘of greatest importance.’’
    • ‘Geographical variation in morphology has been documented in N. mediocris for many years via the recognition of trinomials (subspecies: N. m. mediocris, usambarica, fuelleborni, and bensoni.)’
    • ‘In such instances, you may know, the individuals who make the discovery have the honor of creating the trinomial.’
    • ‘Many invalid trinomials will persist until someone takes the time to quantify them and reassess their validity.’


Late 17th century: from tri- ‘three’, on the pattern of binomial.