Possible Clues:

• Three-line stanza
• Half a sestet, in an Italian sonnet
• Group of three rhyming lines
• Three connected rhymed lines in poetry
• Eschewing even bits of theory, create lines of verse
• Group of three lines
• Three-line rhyme
• Top secret operations going to be sent up in a bit of rhyming verse
• Sonnet-ending unit
• Three lines of verse