What literary form involves a structured set of six words used repeatedly in different lines?

The correct answer is a sestina, which is a highly structured poetic form consisting of six stanzas of six lines each, followed by a three-line envoi. What distinguishes a sestina is its pattern of word repetition; the last words of each of the first six lines are used as the ending words for specific lines in the subsequent stanzas, creating a cyclical and intricate pattern of imagery and theme. This form accentuates the emotional weight of the repeated words and allows for significant depth in exploration of the poem's subject matter.

In contrast, a sonnet is typically a 14-line poem with a specific rhyme scheme and meter, often focusing on themes of love and reflection, but it does not employ the repetitive structure found in a sestina. A haiku is a traditional three-line form consisting of 17 syllables in a 5-7-5 pattern, oriented toward nature and moments of insight, lacking the complexity of repetition and length that a sestina possesses. Free verse, on the other hand, eschews conventional meter and rhyme altogether, allowing poets the freedom to write without a fixed structure, which again does not align with the defined format of a sestina.