An 'Iamb' is a two-syllable word or phrase where, if it was spoken out loud, the stress would be on the second syllable. (For example: 'A horse!')
Iambic Pentameter is five of these strung together. (For example: "A horse! A horse! My kingdom for a horse!") All of the clues in this word ladder are ten syllables long, and the natural stress should be on every second syllable.