Small piece of code lost at first (6)
I believe the answer is:
morsel
'small piece' is the definition.
(I've seen this before)
'code lost at first' is the wordplay.
'code' becomes 'Morse' (Morse code).
'at first' says to take the initial letters.
The first letter of 'lost' is 'l'.
'morse'+'l'='MORSEL'
'of' acts as a link.
(Other definitions for morsel that I've seen before include "Just a fragment of food" , "A tiny bit" , "Crumb" , "Small amount of food, a bite" , "Tidbit" .)