On p 160 of Language on Vacation (1965), Dmitri Borgmann issued the challenge "For the logophile who feels the urge to explore virgin territory, word girders are just the thing." A word girder is constructed by exchanging letters between a pair of words to form another pair of words. Borgmann lists three 5-letter examples.
Word Ways: Vol. 35
, Article 10.
Available at: http://digitalcommons.butler.edu/wordways/vol35/iss4/10