Reckless
Old English reccelēas, from the Germanic base (meaning ‘care’) of reck.
wiktionary
From Middle English rekles, reckeles, rekkeles, (also recheles), from Old English rēcelēas(“reckless, careless, negligent”), equivalent to reck + -less. Cognate with West Frisian roekeleas(“reckless”), Dutch roekeloos(“reckless”), German Low German ruuklos(“careless”), German ruchlos(“careless, notorious”).
etymonline
reckless (adj.)
Middle English recheles, from Old English receleas "careless, thoughtless, heedless," earlier reccileas, literally "not recking (of consequences)" from *rece, recce "care, heed," from reccan "to care" (see reck (v.)) + -less. The same affixed form is in German ruchlos, Dutch roekeloos "wicked."
The root verb reck (Old English reccan) is passing into obscurity; the range of Middle English spellings might reflect uncertainty even then about it, e.g. rechiles, retcheles, recelease, richeles, regeles, reccles, rakeles.