Sincerely
来自Big Physics
Safin（讨论 | 贡献）2022年4月27日 (三) 15:29的版本 （建立内容为“Category:etymology == google == [https://www.google.com.hk/search?q=sincerely+etymology&newwindow=1&hl=en ref] mid 16th century (also in the sense ‘not fal…”的新页面）
mid 16th century (also in the sense ‘not falsified, unadulterated’): from Latin sincerus ‘clean, pure’.
wiktionary
sincere + -ly, from Latin sincērus(“pure, clean, sound”).
etymonline
sincerely (adv.)
1530s, "correctly;" 1550s, "honestly," from sincere + -ly (2). As a subscription to letters, recorded from 1702.
