1. A feather of definitive plumage (the entire feathery covering of a bird) and adornment that also helps streamline and soften body contours of aves or birds, reducing friction in the air and in the water.
2. Etymology: from Greek teleos, "complete" + ptilon, "feather".

The plumage of the newborn chick is downy, called neossoptile; that which follows is termed teleoptile.