Part of TV detective associated with Lewis, primarily (6)
I believe the answer is:
morsel
'part' is the definition.
(eg a morsel of food)
'tv detective associated with lewis primarily' is the wordplay.
'tv detective' becomes 'Morse' (Inspector Morse).
'associated with' is a charade indicator (letters next to each other).
'primarily' suggests taking the first letters.
The first letter of 'lewis' is 'l'.
'morse'+'l'='MORSEL'
'of' acts as a link.
(Other definitions for morsel that I've seen before include "A small amount of food, just a piece" , "Scrap, fragment" , "Tiny piece" , "Just a fragment of food" , "Small amount of food, a bite" .)