Definition of trigonal in English:



  • 1Triangular.

    ‘square or trigonal double-sided inserts’
    • ‘Its morphology is either hexagonal or trigonal.’
    • ‘Rhodochrosite crystallizes in the trigonal class of the hexagonal system and occurs in a number of diverse forms.’
    • ‘The lateral profile is trigonal, and the posterior rostral face convex.’
    • ‘Pezzottaite is trigonal, whereas the other members of the beryl group are hexagonal.’
    • ‘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.’
    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. 1.2 Of 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.’
      • ‘The models explain the trigonal pyramidal shape of fibroblast growth factor and provide a basis for interpretation of protein crystal structures.’
      • ‘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.’
      • ‘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.’
      • ‘Simple binuclear and trinuclear complexes form linear and trigonal arrangements but a tetranuclear complex can occur as a tetrahedron or a cubane structure.’
      • ‘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.’
      • ‘After fusion, the branches relaxed to a configuration connected by trigonal vertices with 120° angles between branches to minimize the local energy.’
      • ‘In an associative transition state a penta-coordinated phosphorus atom would be formed, in a dissociative transition a trigonal metaphosphate.’
      • ‘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.’
      • ‘Such a planar molecule is termed a trigonal planar molecule.’
      • ‘Urinary urgency occurs as a result of trigonal or posterior urethral irritation caused by inflammation, stones, or tumor and is common with cystitis.’


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