The Collaborative International Dictionary
Barbule \Bar"bule\, n. [L. barbula, fr. barba beard.]
A very minute barb or beard.
--Booth.(Zo["o]l.) One of the processes along the edges of the barbs of a feather, by which adjacent barbs interlock. See Feather.
Wiktionary
n. (context ornithology English) Any of the secondary barbs that form a fringe of small projections on a feather.
Usage examples of "barbule".
The barbs have mini-barbs, called barbules, connected by structures called nodes.
Each barb had hundreds of little hooks or barbules on it, by means of which the barbs of the feather were held together.
Daring, having expected a much taller person, had fixed his gaze at a higher mark only to find himself staring at the most ridiculous peacock feather, its quill bare in spots, its barbules missing and its faded black eye quivering, bowing, and winking at him each time the little lady moved.
The barbs have mini-barbs, called barbules, connected by structures called nodes.
Each barb had hundreds of little hooks or barbules on it, by means of which the barbs of the feather were held together.
Now we're going to magnify it some more so we can get a good look at the barbules, for it is the features of the barbules that allow for an identification.
The purpose of down is to trap air, and the finer the barbules, the more streamlined or tapered the nodes, and the more distal the location of the nodes, the more efficient the down is going to be at trapping air.