jackknife
UK[ˈdʒæknaɪf]US[ˈdʒækˌnaɪf]
n
A large pocketknife with a folding blade.
n
A dive in which the body is bent at the waist and then straightened.
v
To double up like a folding knife, especially of an articulated vehicle like a truck when its trailer swings around at a sharp angle.
Morpheme Breakdown
jack
knife
jack
common name/tool
knife
cutting tool
Etymology
The word 'jackknife' is a classic example of a compound formed from two common, concrete English nouns. 'Jack', a name that evolved into a generic term for a laborer or a mechanical aid, combines with 'knife' to denote a sturdy, folding knife suitable for a working man. The semantic logic extends metaphorically: the folding action of the knife's blade inspired the name for the diving maneuver where the body folds at the waist, and later for the dangerous buckling of a truck and trailer, which visually resembles the sudden closing of a folding knife. This progression from a simple tool to descriptive terms for physical actions demonstrates the dynamic, figurative capacity of compound words.
Analysis
Structure: jack (common name/tool) + knife (cutting tool)
- jack: From the Middle English personal name 'Jakke', a diminutive of 'John'. Used generically to denote a common man, a laborer, or various mechanical devices. In this compound, it functions as a generic attributive noun implying common utility or a mechanical action.
- knife: From Old English 'cnīf', of Germanic origin. It functions as the core noun, specifying the object's primary nature as a cutting tool.
Examples
He used his jackknife to cut the rope.
The diver executed a perfect jackknife from the high board.
The truck skidded on the ice and jackknifed, blocking both lanes of the highway.