onset (n.)youdaoicibaDictYouDict[onset 词源字典]
1530s, "attack, assault," from on + set (n.); compare verbal phrase to set (something) on (someone). Weaker sense of "beginning, start" first recorded 1560s. Figurative use in reference to a calamity, disease, etc. is from 1580s.[onset etymology, onset origin, 英语词源]