Romantic laments tiniest failing (14)
I believe the answer is:
sentimentalist
'romantic' is the definition.
(thesaurus)
'laments tiniest failing' is the wordplay.
'failing' is an anagram indicator.
'laments'+'tiniest'='lamentstiniest'
'lamentstiniest' with letters rearranged gives 'SENTIMENTALIST'.
(Other definitions for sentimentalist that I've seen before include "Nostalgic chap" , "Soppy person" , "One who's sloppy" , "Romantic" , "Being overemotional" .)