petal(n = noun.plant) flower petal - part of the perianth that is usually brightly colored;
is a kind of floral leaf
is a part of corolla
Derived form adjective petalous₁

1.  One of the leaves of the corolla, or the colored leaves of a flower. See Corolla, and Illust. of Flower. [1913 Webster]

2.  One of the expanded ambulacra which form a rosette on the black of certain Echini. [1913 Webster]

petal, n. each of the parts of the corolla of a flower.

Derivative:
petaline adj. petalled adj. (also in comb.). petal-like adj. petaloid adj.

Etymology:
mod.L petalum, in LL metal plate f. Gk petalon leaf f. petalos outspread

flower petal