means One of the soft, often colorful segments that make up the showy ring around a flower's reproductive center.

from From the New Latin 'petalum,' lifted from the Greek 'petalon' — meaning a leaf, a thin plate, or anything flat and spread out. That word grows from the root 'petannynai,' 'to spread out,' a cousin of the same spreading-and-flying family that gives us 'feather' and 'pen.' So a petal is, quite literally, a leaf flung open.