MIRAS /ˈmaɪræs, -rəs/ BrE AmE noun [uncountable] abbreviation for
Mortgage Interest Relief at Source; a system used until 2000, in the UK, by which someone who had a ↑ mortgage (=money borrowed from a bank etc to buy a house) was allowed to pay less income tax. The borrower was given ↑ tax relief (=the right to pay less tax) on the ↑ interest that he or she paid on the mortgage, and this reduced the cost of the mortgage payments.