From Longman Dictionary of Contemporary Englishequilateral trianglee‧qui‧lat‧e‧ral tri‧an‧gle /ˌiːkwəlætərəl ˈtraɪæŋɡəl/ noun [countable] technical HMa triangle whose three sides are all the same length

Examples from the Corpus

equilateral triangle• The Vesica piscis On the diameter of a circle an equilateral triangle is described centrally such that its apex just touches the circumference.• The tetrahedron has four faces, each an equilateral triangle.• These two lie close together, and make up an equilateral triangle with Zeta Puppis and Lambda Velorum.• The simplest polygon is the equilateral triangle which echoes itself at 60° intervals.• The equilateral triangle already proclaimed the magic of 3.