Pieta n.

mid-14c., piete (late 12c. as a surname), "mercy, tenderness, pity" (senses now obsolete in this word but preserved in its doublet, pity), from Old French piete "piety, faith; pity, compassion" (12c.), from Latin pietatem (nominative pietas) "dutiful conduct, sense of duty; religiousness, piety; loyalty, patriotism; faithfulness to natural ties," in Late Latin "gentleness, kindness, pity;" from pius "kind" (see pious).

From 1570s in English as "filial affection, dutiful conduct or behavior toward one's parents, relatives, country, etc." Meaning "piousness, faith in and reverence for the Supreme Being" is attested in English from c. 1600. Compare pity (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.