Definition of trigonal in English:



  • 1Triangular.

    ‘square or trigonal double-sided inserts’
    • ‘Its morphology is either hexagonal or trigonal.’
    • ‘The trigonal planar arrangement of the groups around the carbonyl carbon atom enables the carbon atom to be relatively open to attack from above, or below.’
    • ‘Rhodochrosite crystallizes in the trigonal class of the hexagonal system and occurs in a number of diverse forms.’
    • ‘Pezzottaite is trigonal, whereas the other members of the beryl group are hexagonal.’
    • ‘The lateral profile is trigonal, and the posterior rostral face convex.’
    1. 1.1Biology Triangular in cross section.
      ‘large trigonal shells’
      • ‘The triangular habit suggested trigonal symmetry and a possible identification as hilairite or a contact-twinned form of gaidonnayite.’
      • ‘The auricles in early ontogeny are relatively large and distinctly trigonal, with their free margins meeting the hinge line at acute angles.’
      • ‘At the same time, however, it has been reported that the zeta line is constructed to position a thick filament at the trigonal point of the three thin filaments in the opposite sarcomere.’
      • ‘In this case, the c-axis, or axis of trigonal symmetry, is vertical with respect to the organic substrate and hence to the wall itself.’
    2. 1.2Of or denoting a crystal system or three-dimensional geometrical arrangement having three equal axes separated by equal angles that are not right angles.
      • ‘These are, in order of decreasing symmetry, the cubic, hexagonal, tetragonal, trigonal, orthorhombic, monoclinic, and triclinic systems.’
      • ‘Hexagonal crystals (such as aquamarine and emerald) are useful in defining our goals and successes, whilst trigonal crystal systems (ie tourmaline and amethyst) help us to focus on simplicity.’
      • ‘Simple binuclear and trinuclear complexes form linear and trigonal arrangements but a tetranuclear complex can occur as a tetrahedron or a cubane structure.’
      • ‘The broad Bragg peak arises from a cholesterol monolayer embodying poorly ordered two-dimensional crystalline domains, each containing ~ 200 molecules in a proposed trigonal arrangement.’
      • ‘After fusion, the branches relaxed to a configuration connected by trigonal vertices with 120° angles between branches to minimize the local energy.’
      • ‘When the cysteine substrate is bound the geometry changes to a trigonal bipyramid, in which the substrate and the glutamic acid occupy the apical positions.’
      • ‘The second morphotype which comprises all illustrated paratypes, bears an outer cyst surface with trigonal pointed crystal tips.’
      • ‘Upon compression, a cholesterol film transforms from a monolayer of trigonal symmetry and low crystallinity to a trilayer, composed of a highly crystalline bilayer in a rectangular lattice and a disordered top cholesterol layer.’
      • ‘In an associative transition state a penta-coordinated phosphorus atom would be formed, in a dissociative transition a trigonal metaphosphate.’
      • ‘Numerous examples can be found, from trigonal hillocks on diamonds to pits and highly irregular surfaces on crystals that we are accustomed to seeing in simple planar forms.’
      • ‘Urinary urgency occurs as a result of trigonal or posterior urethral irritation caused by inflammation, stones, or tumor and is common with cystitis.’
      • ‘Such a planar molecule is termed a trigonal planar molecule.’
      • ‘The models explain the trigonal pyramidal shape of fibroblast growth factor and provide a basis for interpretation of protein crystal structures.’


Late 16th century from medieval Latin trigonalis, from Latin trigonum (see trigon).