Lacking hope, Hamlet abandons boundaries when wearing frock (9)
I believe the answer is:
dreamless
'lacking hope' is the definition.
(without hopes and dreams)
'hamlet abandons boundaries when wearing frock' is the wordplay.
'abandons boundaries' indicates the central letters (the boundaries of the word are removed).
'when wearing' is an insertion indicator (letters are worn by the letters containing them).
'frock' becomes 'dress' (synonyms).
The centre of 'hamlet' is 'amle'.
'amle' going within 'dress' is 'DREAMLESS'.
(Other definitions for dreamless that I've seen before include "such sound sleep?" , "So deep in sleep" , "Lacking any vision" , "Lacking aspiration" .)