I've seen these same definitions published elsewhere but can't put my finger on where:
https://books.google.com/books?id=bM8ZAwAAQBAJ&pg=PA19&lpg=PA19&dq=civil+war+battle+engagement+skirmish+demonstration&source=bl&ots=KPGFSpOXOn&sig=jlzzCuGCom-HGDBchhw7ae4OZDc&hl=en&sa=X&ved=0ahUKEwjB_Nret7bWAhUFyWMKHcwFB90Q6AEIPDAG#v=onepage&q=civil%20war%20battle%20engagement%20skirmish%20demonstration&f=false