Final answer:
Walt Whitman refers to Abraham Lincoln in "O Captain! My Captain!", an elegy expressing sorrow over the president's assassination with traditional rhyme and meter.
Step-by-step explanation:
Walt Whitman refers to Abraham Lincoln in the poem "O Captain! My Captain!". This poem is one of two that Whitman wrote on the death of Abraham Lincoln and stands out as a moving elegy to the assassinated president.
In contrast to much of Whitman's work which is characterized by free verse and the celebration of everyday life, "O Captain! My Captain!" adopts a more traditional rhyme and meter to convey the poet's deep sorrow over Lincoln's passing.