A back-formation is a word created by removing an element from an existing word. It can change the word’s meaning or the part of speech.
Berserk is a back-formation from berserker, one of a band of
ancient Norse warriors legendary for their savagery and reckless
frenzy in battle.
Pea and plural peas are a back-formation of Middle English
'pease', which was a mass noun in wide use, like oatmeal.
Edit is a back formation of editor. Editor was in use for almost 150
years before edit. Edit arose because the word 'editor' sounds as if
it should mean 'one who edits'.