This article is from the Puzzles FAQ, by Chris Cole email@example.com and Matthew Daly firstname.lastname@example.org with numerous contributions by others.
What exceptional words turn into other words by both insertion and
deletion of letters?
longest word both charitable and hospitable
shortest word both stingy and hostile IMPETUOUS (9)
Unless noted otherwise, all words occur in Webster's Third New International
Dictionary, Merriam-Webster, Springfield, MA, 1961.