pitiless adj.

mid-13c., pite, "compassion, kindness, generosity of spirit;" c. 1300 "disposition to mercy, quality of being merciful," also "a feeling of sympathy and compassion aroused by the sorrow or suffering of another," from Old French pite, pitet "pity, mercy, compassion, care, tenderness; pitiful state, wretched condition" (11c., Modern French pitié), from Latin pietatem (nominative pietas) "piety, loyalty, duty" (see piety). Replaced Old English mildheortness, literally "mild-heartness," itself a loan-translation of Latin misericordia.

It is some comfort to receive commiseration or condolence ; it gives one strength to receive sympathy from a loving heart ; it is irksome to need compassion ; it galls us to be pitied. [Century Dictionary, 1895]

Middle English pity also could mean "devout obedience to God" (mid-14c.), and pity and piety were not fully distinguished until 17c. Transferred sense of "grounds or cause for pity, matter or source of grief or regret" is from late 14c.

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.