The essence of what's locked up in decrepit household (4)
I believe the answer is:
pith
'the essence' is the definition.
('pith' can be a synonym of 'essence')
'in decrepit household' is the wordplay.
'in' indicates a hidden word.
'PITH' is hidden within 'decrepit household'.
'of what's locked up' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for pith that I've seen before include "Soft tissue; essence" , "White tissue in oranges" , "White inner skin of an orange" , "Spongy tissue like that lining an orange skin" , "Tissue inside the rind of citrus fruits" .)