Regret
late Middle English: from Old French regreter ‘bewail (the dead)’, perhaps from the Germanic base of greet2.
wiktionary
From Middle English regretten, from Old French regreter, regrater(“to lament”), from re-(intensive prefix) + *greter, *grater(“to weep”), from Frankish *grātan(“to weep, mourn, lament”), from Proto-Germanic *grētaną(“to weep”), from Proto-Indo-European *ǵʰreh₁d-(“to sound”); and Frankish *greutan(“to cry, weep”), from Proto-Germanic *greutaną(“to weep, cry”), from Proto-Indo-European *gʰrewd-(“to weep, be sad”), equivalent to re- + greet. Cognate with Middle High German grāzan(“to cry”), Old English grǣtan(“to weep, greet”), Old English grēotan(“to weep, lament”), Old Norse gráta(“to weep, groan”), Gothic 𐌲𐍂𐌴𐍄𐌰𐌽( grētan, “to weep”). More at greet.
etymonline
regret (v.)
late 14c., regreten, "to look back with distress or sorrowful longing; to grieve for on remembering," from Old French regreter "long after, bewail, lament someone's death; ask the help of" (Modern French regretter), from re-, intensive prefix (see re-), + -greter, which is possibly from Frankish or some other Germanic source (compare Old English grætan "to weep;" Old Norse grata "to weep, groan"), from Proto-Germanic *gretan "weep." "Not found in other Romance languages, and variously explained" [Century Dictionary].
From 1550s as "to grieve at (an event, action, revelation of facts, etc.)." Related: Regretted; regretting. Replaced Old English ofþyncan, from of- "off, away," here denoting opposition, + þyncan "seem, seem fit" (as in methinks).
regret (n.)
1530s, "complaint, lament," a sense now obsolete, from the verb, or from French regret, back-formation from regreter "long after, bewail" (see regret (v.)).
From 1590s as "pain or distress in the mind due to some external circumstances" (as in to look on (something) with regret); 1640s as "pain or distress in the mind at something done or left undone." In correspondence, in declining an invitation, etc., regrets "expressions of regret, intimation of regret for inability to do something" is attested by 1851.
