"Breadthening" is a word that is not commonly used, but its spelling can be explained with IPA phonetic transcription. The word is spelled with an "e" after the "d" because it represents a sound similar to the "th" sound in "brother". The "en" at the end of the word is pronounced as an "un" sound, while the "ing" is pronounced as the familiar "-ing" ending found in many verbs. The word "breadthening" means expanding or increasing the breadth or scope of something.