tertiarily

This term is used to establish a strict hierarchy of importance or a chronological sequence, specifically designating the third level. It is most common in academic, legal, or technical writing where a precise, tiered structure of arguments or priorities is required.

Because of its high level of formality, it is rarely used in spoken English or casual correspondence. In most everyday contexts, speakers prefer phrases such as "thirdly" or "in the third place" to avoid sounding overly stiff or pedantic.