piety n.

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.

mid-15c., "having or intended to show faith in and reverence for the Supreme Being," from Latin pius "dutiful, devout, conscientious, religious; faithful to kindred; inspired by friendship, prompted by natural affections," perhaps [de Vaan, Klein] related to Latin purus "pure, clean," via a PIE *pu-io- "purifying" (see pure), but the exact development is disputed.

The classical Roman sense of "having or exhibiting due respect and affection for parents and others to whom such is due" is attested in English from 1620s. In the religious sense, sometimes denoting practice under pretense of religion or for good ends (1630s) and in this sense often coupled with fraud (n.). Related: Piously; piousness.