Desperately hard up in seclusion (6)
I believe the answer is:
purdah
'seclusion' is the definition.
(purdah is a system of seclusion for women)
'desperately hard up' is the wordplay.
'desperately' is an anagram indicator.
'hard'+'up'='hardup'
'hardup' with letters rearranged gives 'PURDAH'.
'in' acts as a link.
(Other definitions for purdah that I've seen before include "Eastern tradition of keeping women secluded" , "Screening curtain; seclusion" , "Period of seclusion" , "Hindu or Muslim seclusion of women" , "Women's seclusion" .)