Jackknife
/ˈdʒæk.naɪf/noun
A folding knife with a blade that folds into the handle, or a sudden diving motion with the body bent sharply at the waist.
Did you know?Jackknife is an English compound built from the common name Jack plus knife; the eerie part is that the same word was later reused for a sudden, folded diving motion because the body snaps like a blade closing shut.
Etymological Timeline
Middle English
English
Jack
“A common male name and nickname for an ordinary fellow or servant”
Old French
French
Jacques
“The name James, widely used as a familiar personal name”
Late Old English
English
næf
“Knife or cutting blade”
Old English
English
cnīf
“Knife, blade”
Modern English
English
jackknife
“A folding knife, and by extension a sharp folding motion of the body or an object”