What entity name is that, and what non-bold Unicode character does it correspond to?  There are already a lot of mathematical bold characters including Latin letters, digits, some Greek and symbols.

In addition, these are also available in mathematical bold fraktur, bold italic, bold script, double-struck ("blackboard bold"), fraktur, italic, monospace, sans-serif, sans-serif bold, sans-serif bold italic, sans-serif italic, and script.  These are for mathematical use only, though some bad persons have used them to smuggle these font faces into plain text situations (the resulting kerning is usually terrible).