Writer sadly lost plaything (7)
I believe the answer is:
tolstoy
'writer' is the definition.
(I've seen this before)
'sadly lost plaything' is the wordplay.
'sadly' indicates an anagram.
'plaything' becomes 'toy' (synonyms).
'lost' is an anagram of 'tols'.
'tols'+'toy'='TOLSTOY'
(Other definitions for tolstoy that I've seen before include "Lost toy belonging to Count Leo, writer" , "Great Russian author of 'War and Peace'" , "Lost toy of the Russian author" , "Count Leo . . . . . . ., author of 'War and Peace'" , "Author of Anna Karenina, d.1910" .)