Lewis & Short

pĭo, āvi, ātum, 1, v. a. [pius].

  1. I. To seek to appease, to appease, propitiate by sacrifice (syn. place).
    1. B. Lit.: Silvanum lacte piabant, Hor. Ep. 2, 1, 143: ossa, Verg. A. 6, 379: busta (i.e. Manes), Ov. M. 13, 515: Janus Agonali luce piandus erit, id. F. 1, 318.
  2. II. Transf.
    1. A. To honor with religious rites, to celebrate: ubi piem Pietatem, Plaut. As. 3, 1, 3: aras ture, Prop. 3, 10 (4, 9), 19: in magicis astra piare focis, to perform sacred rites, id. 1, 1, 20.
    2. B. To purify with sacred rites (syn.: procuro, lustro): si quid tibi piandum fuisset, Cic. Dom. 51.
    3. C. To make or seek to make good, to atone for, expiate: damna, Ov. A. A. 3, 160: mors morte pianda est, id. M. 8, 483: fulmen, to avert by sacrifice the misfortune portended by lightning, id. F. 3, 291: nefas triste, to atone for, avert the penalty, Verg. A. 2, 184; Ov. H. 19, 194: cometes terrificum sidus, ac non leviter piatum, Plin. 2, 25, 23, § 92.
    4. D. To punish, avenge: culpam morte, Verg. A. 2, 140: grande nefas et morte piandum, Juv. 13, 54.
    5. E. To free from madness, Fest. p. 213 Müll.: jube te piari de meā pecuniā: nam ego quidem insanum te esse certo scio, Plaut. Men. 2, 2, 17; so id. ib. 3, 2, 51.