If HTML does not have a standard name for a character, I normally turn to DocBook next. Its entity names are based on the standard SGML entity names. (These are among the SGML features that got dropped out of XML in the process of making it simple enough for mere mortals to use.) They aren't as well known as the HTML entity names, but they are much more comprehensive and are an international standard. The SGML entity names include those listed below.

ISO 8879:1986//ENTITIES Added Math Symbols: Arrow Relations//EN//XML

ISO 8879:1986//ENTITIES Added Math Symbols: Binary Operators//EN//XML

ISO 8879:1986//ENTITIES Added Math Symbols: Delimiters//EN//XML

ISO 8879:1986//ENTITIES Added Math Symbols: Negated Relations//EN//XML

ISO 8879:1986//ENTITIES Added Math Symbols: Ordinary//EN//XML

ISO 8879:1986//ENTITIES Added Math Symbols: Relations//EN//XML

ISO 8879:1986//ENTITIES Box and Line Drawing//EN//XML

ISO 8879:1986//ENTITIES Russian Cyrillic//EN//XML

ISO 8879:1986//ENTITIES Non-Russian Cyrillic//EN//XML

ISO 8879:1986//ENTITIES Diacritical Marks//EN//XML

ISO 8879:1986//ENTITIES Greek Letters//EN//XML

ISO 8879:1986//ENTITIES Monotoniko Greek//EN//XML

ISO 8879:1986//ENTITIES Greek Symbols//EN//XML

ISO 8879:1986//ENTITIES Alternative Greek Symbols//EN//XML

ISO 8879:1986//ENTITIES Added Latin 1//EN//XML

ISO 8879:1986//ENTITIES Added Latin 2//EN//XML

ISO 8879:1986//ENTITIES Numeric and Special Graphic//EN//XML

ISO 8879:1986//ENTITIES Publishing//EN//XML

ISO 8879:1986//ENTITIES General Technical//EN//XML