Threaten to chase the woman pinching one’s valuable property (8)
I believe the answer is:
'valuable property' is the definition.
(I know that heirloom are usually the valuable)
'threaten to chase the woman pinching one's' is the wordplay.
'threaten' becomes 'loom' (something threatening might loom over you).
'to chase' says to put letters next to each other (some letters chase after others).
'the woman' becomes 'her' (her refers to a woman).
'pinching' indicates putting letters inside (taking inside).
'one' becomes 'i' (Roman numeral).
'her' enclosing 'i' is 'heir'.
'loom' after 'heir' is 'HEIRLOOM'.
(Other definitions for heirloom that I've seen before include "Object passed down through a family for generations" , "one long in the family" , "Possession handed down through several generations of family" , "Something that has been in a family for generations" , "Valuable family piece" .)