hardly (adv.)youdaoicibaDictYouDict[hardly 词源字典]
c. 1200, "in a hard manner, with great exertion or effort," from Old English heardlice "sternly, severely, harshly; bravely; excessively" (see hard (adj.) + -ly (2)). Hence "assuredly, certainly" (early 14c.). Main modern sense of "barely, just" (1540s) reverses this, via the intermediate meaning "not easily, with trouble" (early 15c.). Formerly with superficial negative (not hardly). Similar formation in Old Saxon hardliko, German härtlich, Old Danish haardelig.[hardly etymology, hardly origin, 英语词源]
stern (adj.)youdaoicibaDictYouDict
Old English styrne "severe, strict, grave, hard, cruel," from Proto-Germanic *sternijaz (cognates: Middle High German sterre, German starr "stiff," störrig "obstinate;" Gothic andstaurran "to be stiff;" Old Norse stara; Old English starian "to look or gaze upon"), from PIE root *ster- (1) "rigid, stiff" (see stereo-). Related: Sternly; sternness.