Unfinished model drum (6)
I believe the answer is:
patter
'drum' is the definition.
(thesaurus)
'unfinished model' is the wordplay.
'unfinished' means to remove the last letter.
'model' becomes 'pattern' (pattern is a kind of model).
'pattern' with its last letter taken away is 'PATTER'.
(Other definitions for patter that I've seen before include "Noise of fast light steps" , "Rapid and glib speech, perhaps in selling" , "Salesman's chat - walk with quick, soft steps" , "Sales talk or sounds of little feet" , "Rapid and glib talk" .)