Droop when encountering a lengthy account (4)
I believe the answer is:
saga
'lengthy account' is the definition.
(a saga is a lengthy narrative)
'droop when encountering a' is the wordplay.
'droop' becomes 'sag' (synonyms).
'when encountering' says to put letters next to each other.
'sag'+'a'='SAGA'
(Other definitions for saga that I've seen before include "Icelandic or Norse story" , "Tale of heroes" , "Norse narrative" , "Long and involved story" , "Body of legend" .)