Cutting off end of piece and unravelling yarn in two parts (6)
I believe the answer is:
binary
'in two parts' is the definition.
(binary means made up of two parts or elements)
'cutting off end of piece and unravelling yarn' is the wordplay.
'cutting off end of piece' becomes 'bi' (I can't explain this - if you can you should believe this answer much more).
'and' means one lot of letters go next to another.
'unravelling' indicates anagramming the letters.
'yarn' with letters rearranged gives 'nary'.
'bi'+'nary'='BINARY'
(Other definitions for binary that I've seen before include "A system of two stars" , "A sort of star" , "Arithmetic system to the base of 2 as used by computers" , "Involving two things" , "Two-star system" .)