Tense silence during increased security (8)
I believe the answer is:
mortgage
'security' is the definition.
(as in security on a loan)
'tense silence during increased' is the wordplay.
'tense' becomes 't' (abbreviation used in many dictionaries).
'silence' becomes 'gag' (gagging is a kind of silencing).
'during' indicates putting letters inside.
'increased' becomes 'more'.
't'+'gag'='tgag'
'tgag' put within 'more' is 'MORTGAGE'.
(Other definitions for mortgage that I've seen before include "Temporary conveyance of property as security against a loan" , "Loan secured against property" , "Money-lending agreement" , "Transfer of property rights as security for a loan" , "Home loan" .)