The most common and most likely answer to this crossword clue is the 8 plus 4 letter word PARADISE LOST
I've seen this crossword clue in The Times
P
A
R
A
D
I
S
E
L
O
S
T
More clues leading to the result PARADISE LOST
- Adlestrop is a fantastic work of poetry
- Ideal spot, as sullied, Tempter at last having entered?
- Broadcast serial, top sad epic
- Poem excited ladies so in actor’s words
- Epic row about one son splitting fortune with another
- Reworked pastor’s ideal religious text
- Poem is read to pals wrongly
- In poem airborne soldier dies horribly, way off course
Buddy explains!

The straight part
We know that "poem" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case poem = paradise lost.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.