The Latin adjective peregrīnus meant "coming from foreign parts" and is perhaps derived from per- (through) + ager (field, territory, land, country). By the 5th century this word was also being used to specifically describe people who travelled to visit religious sites. The Norman French squished this word down and changed the r to an l, resulting in
pilegrin, and ultimately pilgrim. (In Central France, they squished it even further into pèlerin.)
Meanwhile, however, Latin was still a living language throughout the Middle Ages, so the original form also survived, particularly in reference to the falcons which were most highly prized for hunting because of their speed and accuracy. Why were they called falco peregrinus? Since peregrine falcons build their nests on high, inaccessible crags (more latterly on high-rise buildings!), falconers could not get at them in order to steal the young ones. They had to wait and catch them during the bird's migration -- its "pilgrimage", in effect.
"Peregrination" also originally had this sense of "pilgrimage", but by the 1500s it was already being used in its current sense of "travelling or wandering about; coming and going."
Wherever your peregrinations may take you on this holiday weekend, I wish all my American readers a happy Thanksgiving.
Why is a turkey called a turkey? Click here.
For the story on "Black Friday", click here.