Inferior part of row or series (5)
I believe the answer is:
worse
'inferior' is the definition.
(I've seen this before)
'part of row or series' is the wordplay.
'part of' indicates a hidden word.
'WORSE' can be found hidden inside 'row or series'.
(Other definitions for worse that I've seen before include "Less favourable" , "Less satisfactory" , "Less good" , "less moral?" , "More awful or unwell" .)