An eggshell is what remains when two different pairs of identical consonants are removed from a word. Consequently, E S H E is an eggshell which results from the exclusion of two "G"s and two "E"s from the word EGGSHELL.
Word Ways: Vol. 45
, Article 19.
Available at: http://digitalcommons.butler.edu/wordways/vol45/iss4/19