It limits the movement of stock (6)
I believe the answer is:
tether
'stock' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'it limits the movement' is the wordplay.
'it' becomes 'ter' (I can't justify this - if you can you should give a lot more credence to this answer).
'limits' indicates putting letters inside (limit can mean to contain or block off).
'movement' is an anagram indicator.
'the' anagrammed gives 'eth'.
'ter' enclosing 'eth' is 'TETHER'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for tether that I've seen before include "Hold by a rope" , "End of ones --" , "Rope to hobble grazing animal" , "Restrain within limits" , "Rope for tying animal" .)