mega-annumWiktionary 原文构词拆分mega-前缀(originally) Very large, great. · In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by one million (106).+annum词根/词干词源说明From mega- + annum.释义（英文）名词 NounSynonym of megayear: a period of 1 million years.词族相关词（3）MYAMyamya