Which phrase is used to create a play on words, or pun, in “Do Not Go Gentle into That Good Night”?

In Dylan Thomas's poem "Do Not Go Gentle into That Good Night," the phrase that is often highlighted for creating a play on words or pun is "good men." This phrase plays on the contrast between the conventional idea of "good" and the struggle against death. The repeated use of "good" alongside the themes of mortality and resistance contributes to the poem's depth and complexity.