Ébauche
Ébauche is a loanword from French, meaning blank, outline or sketch.
In arts it is a preliminary underpainting or quick sketch in oils for an oil painting.
Horology, clockmaking and watchmaking appropriated the term ébauche to refer to an incomplete or unassembled watch movement and its associated components.
The French term is regularly used by English-speaking artists and art historians, as well as horologists and hobbyists.