Trim old penny black (5)
I believe the answer is:
dinky
'trim' is the definition.
(thesaurus)
'old penny black' is the wordplay.
'old penny' becomes 'd'.
'black' becomes 'inky' ('inky' can be similar in meaning to 'black'**).
'd'+'inky'='DINKY'
(Other definitions for dinky that I've seen before include "Neat and dainty" , "Small, neat and cute" , "Attractively small" , "Dainty (colloq.)" .)