The most common and most likely answer to this crossword clue is the 3 plus 5 letter word EYE RHYME
I've seen this crossword clue in The Times
E
Y
E
R
H
Y
M
E
Buddy explains!
The straight part
We know that "Poetic device exemplified in Keats and Yeats?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case poetic device exemplified in keats and yeats? = eye rhyme.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.