One laid out as an epic poem (5)
I believe the answer is:
iliad
'an epic poem' is the definition.
(Iliad is an example)
'one laid out' is the wordplay.
'one' becomes 'i' (Roman numeral).
'out' is an anagram indicator (out can mean wrong or inaccurate).
'laid' is an anagram of 'liad'.
'i'+'liad'='ILIAD'
'as' is the link.
(Other definitions for iliad that I've seen before include "tale of woes" , "Homer's ancient Greek epic" , "City investment story" , "long story" , "Work on war" .)