(humorous) Any word beginning with w that is not normally taboo but is considered (often humorously) to be so in the given context.
1989, Grant Naylor, Red Dwarf: Infinity Welcomes Careful Drivers:
'We're going mining,' said Lister. 'We're not in the heats of "Come Jiving", we're going to work.' 'Hey - I do not do the "W" word.' 'We're all doing the "W" word,' said Lister.