Lock turning in dresser thankfully (5)
I believe the answer is:
tress
'lock' is the definition.
(I've seen this before)
'turning in dresser thankfully' is the wordplay.
'turning' says the letters should be written in reverse.
'in' says the answer is hidden in the clue.
'ssert' can be found hidden inside 'dresser thankfully'.
'ssert' back-to-front is 'TRESS'.
(Other definitions for tress that I've seen before include "Bit of hair" , "is a bit of a shock" , "Long piece of hair" , "Long lock or plait of hair" , "Braid of hair" .)