When it comes to expressing the topic or subject being discussed, using different synonyms for the phrase "in matter of" can add variety and interest to your language. Some possible synonyms that you could use include "concerning," "regarding," "referring to," "pertaining to," or "touching on." Each of these phrases can be used interchangeably with "in matter of" to convey the same meaning in different words. By experimenting with these synonyms, you can expand your vocabulary and make your writing or speaking more engaging and expressive.