A metrical unit with unstressed-stressed-unstressed syllables is a poetic device known as an IAMB. An IAMB is composed of two syllables, the first being unstressed and the second being stressed. The three solutions to the crossword are IAMB (4 letters), IAMBUS (6 letters) and iambi (5 letters). IAMB is the most common form of iambic meter, while IAMBUS is a longer form of iambic meter, and iambi is a rarer form of iambic meter.