A fletcher is / was / will haven been (sorry DA) an arrow-maker, I think. The little feathers are called fleche or something in French. ICLIU. Not sure about the verb; maybe bowing. An arrow has three feathers with a 120 degree angle between each. A notch in the tail of the arrow allows it to be placed in the bow two different ways. It should be placed such that the angle, rather than the feather, is on the bow side. IT is certainly plausible that the term "cock-up" could derive from doing this incorrectly.