Vaguely stop and read line in poem (9)
I believe the answer is:
Here is my best explanation:
'poem' is the definition.
(Edward Thomas poem)
'vaguely stop and read line' is the wordplay.
'vaguely' indicates an anagram.
'and' means one lot of letters go next to another.
'line' becomes 'l'.
'stopreadl' is an anagram of 'ADLESTROP'.
'in' acts as a link.
(Another definition for adlestrop that I've seen is "where Thomas's train halted".)