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Blend ofr(an arbitrarily chosen initial letter) +Ancient Greekἐννέα(ennéa,“nine”) +-a(to match the final letter of the SI prefixes frommega- upwards).
Coined by Richard J. C. Brown and adopted by theGeneral Conference on Weights and Measures in 2022 as an expansion to themetric prefixes beyond 10±24.
Some popular unofficial terms already in use werehella-,bronto- andxenna-, but terms beginning with the same letters as existing prefixes were considered undesirable, as were as those beginning with common scientific letters such asb orx. Richard J. C. Brown suggested that the new terms begin withr andq, due to their rarity asunit symbols, and that the trends followed by the other prefixes be continued: that they be based on Latin or Greek; that large prefixes end with-a and small prefixes end with-o; that they should be in corresponding large and small pairs; and that the first letters of each prefix should be in reverse alphabetical order (as has been the case for the newer prefixes). He therefore suggestedronna- andronto- (evoking Ancient Greekἐννέα(ennéa) and Latinnovem(“nine”)), andquecca- andquecto- (evoking Ancient Greekδέκα(déka) and Latindecem(“ten”)), because as 1027 and 1030 when written have nine and ten groups of zeroes, respectively. These were adopted, withquecca- changed toquetta-.[1][2]
ronna-
