One’s working with old rope (5)
I believe the answer is:
noose
'rope' is the definition.
(noose is a kind of rope)
'one's working with old' is the wordplay.
'working with' is an anagram indicator (working with the letters).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ones' anagrammed with 'o' can make 'NOOSE'.
(Other definitions for noose that I've seen before include "Loop at the end of a rope" , "Fatal device" , "Catcher" , "Circular loop" , "Catch" .)