The Nuttall Encyclopedia
A metrical foot, consisting of two syllables, of which the first is short and the second long, or in which the stress is on the second.
Wood, James, ed. Entry for 'Iambus'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/i/iambus.html. Frederick Warne & Co Ltd. London. 1900.