1590s, "indifferent, not heeding or looking," from regard (n.) + -less. As elliptical for "regardless of consequences, expenses, etc.," from 1872. Regardful is attested from 1580s. Related: Regardlessly; regardlessness.
mid-14c., "a consideration; a judgment," from Old French regard, regart, from regarder "take notice of," from re-, here perhaps an intensive prefix, + garder "look, heed," from a Germanic language (see guard (n.)).
Meanings "a look, appearance; respect, esteem, favor, kindly feeling which springs from a consideration of estimable qualities" all are recorded late 14c. Phrase in regard to is from mid-15c. (Chaucer uses at regard of).
word-forming element meaning "lacking, cannot be, does not," from Old English -leas, from leas "free (from), devoid (of), false, feigned," from Proto-Germanic *lausaz (cognates: Dutch -loos, German -los "-less," Old Norse lauss "loose, free, vacant, dissolute," Middle Dutch los, German los "loose, free," Gothic laus "empty, vain"), from PIE root *leu- "to loosen, divide, cut apart." Related to loose and lease.
<a href="https://www.etymonline.com/word/regardless">Etymology of regardless by etymonline</a>
Harper, D. (n.d.). Etymology of regardless. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/regardless