Peony, n. [OE. pione, pioine, pioni, OF. pione, F. pivoine, L. paeonia, Gr. paiwni`a, fr. Pai`wn, Paia`n, the god of healing. Cf. Pæan.].
A plant, and its flower, of the ranunculaceous genus Pæonia. Of the four or five species, one is a shrub; the rest are perennial herbs with showy flowers, often double in cultivation. [1913 Webster]
Peony, n. (also paeony) (pl. -ies) any herbaceous plant of the genus Paeonia, with large globular red, pink, or white flowers, often double in cultivated varieties.
Etymology
OE peonie f. L peonia f. Gk paionia f. Paion, physician of the gods