back-formations
A shorter word cut from a longer one.
A back-formation is a shorter word formed by removing an ending from a longer word, or from what looks like an ending. Edit comes from editor. Diagnose comes from diagnosis. Many of these verbs are now standard. Some are still casual. Use the older verb when the shorter form is still casual.
Examples
Use She edited the brief.
Use The lab diagnosed the fault.
Avoid They need to conversate before Friday. (use converse)