Dmitri Borgmann's Language on Vacation includes the following tibit concerning wordplay and the telephone dial: "It appears that the longest word which can be dialed using only letters that appear with odd numerals is WELL-EXPRESSED, and that... with even numerals NONCOMMUNICATING." It seems to us that the first example is an adjectival phrase; the longest single words appear to be PERPLEXEDLY or SLEEPLESSLY. (If you want a longer adjectival phrase, consider the sentence "SELFLESSLY-DEFERRED pleasures are often the best kind.") We can't quibble with the second example except to point out that NONCONTAMINATING ties it for length.
Keith, Michael and Mroice, Dave
"Let Your Fingers Do The Wordplay,"
Word Ways: Vol. 32
, Article 3.
Available at: https://digitalcommons.butler.edu/wordways/vol32/iss2/3