The word "jackknife" is spelled with two K's, although only one is pronounced. The IPA phonetic transcription for "jackknife" is /ˈdʒæknaɪf/. The "j" sound at the beginning of the word is pronounced like "dge" in "edge". The "a" sound in the first syllable is pronounced like "a" in "cat", while the "i" sounds like "eye". The second syllable is pronounced with a long "i" sound like "ife", and the "k" at the end of the word is not pronounced.
Jackknife is a noun that refers to a type of folding knife that has a blade that folds into its handle. It is typically small and compact, making it convenient for carrying in one's pocket. The blade of a jackknife is commonly sharp and may be used for various tasks such as cutting ropes, opening packages, or preparing food. The handle of a jackknife is usually made of metal or plastic and may also contain additional tools or implements like a bottle opener, screwdriver, or corkscrew, depending on the design.
The term "jackknife" can also be used as a verb, which describes a specific diving technique in swimming or an abrupt maneuver performed by a vehicle. When referring to swimming, jackknifing refers to a diving position where the diver leaps into the air, bends their body in half, and brings their knees close to their chest before entering the water. In the context of vehicles, jackknifing describes the action of a vehicle, typically a truck or trailer, where the vehicle's cab and the trailer it is hauling fold together, resembling the shape of a folding knife. This type of situation often occurs when the wheels of the vehicle lock or when excessive force is applied to the brakes, causing the trailer to swing abruptly and misalign with the cab.
The word "jackknife" has an interesting etymology. It comes from the combination of two separate words: "jack" and "knife".
The first part, "jack", originally referred to a type of knife with a folding blade. This term was derived from the Middle English word "jak", which meant a small knife or dagger. The word "jak" ultimately came from the Old French word "jacques", meaning a knife used by peasants.
The second part, "knife", is a common noun that refers to a cutting tool with a sharp blade. The word "knife" has Old English roots, likely derived from the Proto-Germanic word "knīƀaz".
When combined, "jackknife" refers to a specific type of folding knife, characterized by a folding blade that fits into the handle, allowing for easy storage and portability.