In baseball, a speedy runner can sometimes transform a single into a double by "turning up the jets." An analogous metamorphosis in the world of wordplay creates a new specimen from an old one by replacing one of its interior letters with two copies of the same. For instance, GRIPE becomes GRIPPE when the letter "P" is doubled up.
Word Ways: Vol. 48
, Article 9.
Available at: http://digitalcommons.butler.edu/wordways/vol48/iss2/9