Japanese Pac-Man flyer, circa 1980.
The original Japanese title was Pakkuman (パックマン), inspired by the Japanese onomatopoeic slang phrase paku-paku taberu (パクパク食べる), where paku-paku describes (the sound of) the mouth movement when widely opened and then closed in succession. (…) The result was a game named Puck Man.
Later in 1980, the game was picked up for manufacture in the United States by Bally division Midway, which changed the game’s name from Puck Man to Pac-Man in an effort to avoid vandalism to the letter ‘P’. [info from Wikipedia]