Watch online series, Dead Smooth (11)
I believe the answer is:
streamlined
'smooth' is the definition.
(thesaurus)
'watch online series dead' is the wordplay.
'watch online' becomes 'stream' (I've seen this in another clue).
'series' becomes 'line' (line is a kind of series).
'dead' becomes 'd' (abbreviation in government records).
'stream'+'line'+'d'='STREAMLINED'
(Other definitions for streamlined that I've seen before include "Designed for smooth flow" , "Shaped for speed" , "made more efficient" , "Of sleek appearance" , "Aerodynamic" .)