Girl has old bit of rope (5)
I believe the answer is:
lasso
'rope' is the definition.
(I know that rope can be written as lasso)
'girl has old bit of' is the wordplay.
'girl' becomes 'lass' (lass can informally mean a girl).
'has' is a charade indicator (letters next to each other).
'bit of' says to take the initial letters.
The first letter of 'old' is 'o'.
'lass'+'o'='LASSO'
(Other definitions for lasso that I've seen before include "Rope used for catching cattle" , "A cowboy's rope with a running noose" , "Belgian composer" , "Nosed rope" , "Ling-nosed rope" .)