Woefully speak about diamonds left (5)
I believe the answer is:
sadly
'woefully' is the definition.
(thesaurus)
'speak about diamonds left' is the wordplay.
'speak' becomes 'say' (I've seen this before).
'about' indicates putting letters inside.
'diamonds' becomes 'd' (abbreviation for the card suit diamonds).
'left' becomes 'L' (common abbreviation).
'd'+'l'='dl'
'say' going around 'dl' is 'SADLY'.
(Other definitions for sadly that I've seen before include "Alas" , "I regret to say" , "Mournfully" , "Regrettably" , "Lamentably, unfortunately" .)