Anineteen-line poem divided into five tercets and a final quatrain. the only two rhymes which are repeated as follows: aba, aba, aba, aba, aba, abaa. line 1 is repeated entirely to form lines 6, 12, and 18, and line 3 is repeated entirely to form lines 9, 15, and 19; thus, eight of the nineteen lines are refrain. dylan thomas’s poem "do not go gentle into that good night" is an example of this as is plath’s "mad girl’s love song

The answer is villanelle.

Explanation:

A villanelle is a nineteen-line poem, constituted of five tercets and a quatrain. The rhyming scheme for those lines is: aba, aba, aba, aba, aba, abaa. Some lines are repeated throughout the poem. The repeated lines are called refrains. Thus, the description given in the question is that of a villanelle. Let's check those characteristics in Dylan Thomas's poem "Do Not Go Gentle Into That Good Night":

(First tercet)

Do not go gentle into that good night,  A

Old age should burn and rave at close of day;  B

Rage, rage against the dying of the light. A

(Second tercet)

Though wise men at their end know dark is right,  A

Because their words had forked no lightning they  B

Do not go gentle into that good night.  A

(Third tercet)

Good men, the last wave by, crying how bright  A

Their frail deeds might have danced in a green bay,  A

Rage, rage against the dying of the light.  A

(Fourth tercet)

Wild men who caught and sang the sun in flight,  A

And learn, too late, they grieved it on its way,  B

Do not go gentle into that good night.  A

(Fifth tercet)

Grave men, near death, who see with blinding sight  A

Blind eyes could blaze like meteors and be gay,  B

Rage, rage against the dying of the light.  A

(Quatrain)

And you, my father, there on the sad height,  A

Curse, bless, me now with your fierce tears, I pray.  B

Do not go gentle into that good night.  A

Rage, rage against the dying of the light. A

Rhyming scheme: night and the words that rhyme with it - A; day and the words that rhyme with it - B.

Refrains: "Do not go gentle into that good night" and "Rage, rage against the dying of the light".