It just ain't so. I copied this from Snopes.com
The piece
quoted above is silly, and so obviously a joke that shouldn't need any debunking. Nonetheless, so many have forwarded it to us accompanied by an "Is this true?" query that we feel duty-bound to provide a bit of historical and linguistic information to demonstrate why this story couldn't possibly be true.
First of all, despite the lack of motion pictures and television way back in the 15th century, the details of medieval battles such as the one at Agincourt in 1415 did not go unrecorded. Battles were observed and 
chronicled by heralds who were present at the scene and recorded what they saw, judged who won, and fixed names for the battles. These heralds were not part of the participating armies, but were, as military expert John Keegan describes, members of an "international corporation of experts who regulated civilized warfare." Several heralds — both French and English — were present at the battle of Agincourt, and not one of them (or any later chroniclers of Agincourt) mentioned anything about the French having cut off the fingers of captured English bowman.
Secondly, for a variety of reasons, it made no military sense whatsoever for the French to capture English archers, then mutilate them by cutting off their fingers. Medieval warriors did not take prisoners because they were observing a moral code that dictated that opponents who laid down their arms and ceased fighting must be treated humanely; they took prisoners because high-ranking captives were valuable property that could be ransomed for money. The ransoming of prisoners was the only way for medieval soldiers to make a quick fortune, and so they seized every available opportunity to capture opponents who could be exchanged for a handsome price.
Bowman were not valuable prisoners, though; they stood outside the chivalric system and were considered the social inferiors of men-at-arms. There was no monetary reward to be obtained by capturing them, nor was there any glory to be won by defeating them in battle. As Keegan wrote, "To meet a similarly equipped opponent was the occasion for which the armoured soldier trained perhaps every day of his life from the onset of manhood. To meet and beat him was a triumph, the highest form which self-expression could take in the medieval nobleman's way of life." Archers were not the "similarly equipped" opponents that armored soldiers triumphed in defeating; if the two clashed in combat, the armored soldier would either kill an archer outright or leave him to bleed to death rather than go to the wasteful effort of taking him prisoner.
Moreover, if archers could be ransomed, then cutting off their middle fingers would be a senseless move. Your opponent is not going to pay you (or pay you much) for the return of mutilated soldiers, so now what do you do with them? Take on the burden and expense of caring for them? Kill them outright and violate the medieval moral code of civilized warfare? (Henry V was heavily criticized for supposedly having ordered the execution of French prisoners at Agincourt.)
Even if killing prisoners of war did not violate the moral code of the times, what would be the purpose of cutting off fingers and then executing these same people? Why not simply kill them outright in the first place? Do you return these prisoners to your opponents in exchange for nothing, thereby providing them with trained soldiers who can fight against you another day? (Even if archers whose middle fingers had been amputated could no longer effectively use their bows, they were still capable of wielding mallets, battleaxes, swords, lances, daggers, maces, and other weapons, as archers typically did — and as they indeed did at Agincourt — when the opponents closed ranks with them and the fighting became hand-to-hand.)
Possibly the most telling points against this story center on the bow itself. The English longbow was traditionally constructed of ash, not yew. Though if ash were not available, other woods might be used in place of it, none of those replacement woods would be yew. Yew was considered terribly unlucky, being known as the 'funeral tree,' and wreaths of it were traditionally laid on coffins or boughs of it buried with the deceased. Bringing yew into the home of the living was considered equivalent to inviting death to take one of the household members within the year -- that's how strong the prohibition against having it around went. To fashion a weapon of this material and carry it into battle where every scrap of good luck was going to be needed would be unthinkable.
Moreover, yew is poisonous. Handling a bow made of this material might cost you your life if you ever forgot to wash your hands before taking your dinner.
So much for history. There's not much that makes linguistic sense here, either. The claim that the "difficult consonant cluster at the beginning" of the phase 'pluck yew' has "gradually changed to a labiodental fricative 'f'" is specious. A labiodental fricative was no less "difficult" for Middle English speakers to pronounce than the aspirated bilabial stop/voiceless lateral combination of 'pl' that the fricative supposedly changed into, nor are there any other examples of such a shift occurring in English. As well, the etymology of the word '****' indicates that the word originated in a completely different time, place, and manner than the absurd version presented here. And on top of all that, the insulting gesture of extending one's middle finger (digitus impudicus in Latin) dates from Roman times (at least 2,000 years ago), so it obviously was not developed in conjunction with the creation of the English word '****.'"
Last but certainly not least, wouldn't these insolent archers have been bragging about plucking the bow's string, and not the wood of the bow itself?
Barbara "bowfinger" Mikkelson