Definition

1. Noun:
   • A mechanical joint allowing movement in one plane only: A pin joint, often used in engineering, that connects two rods or parts and permits angular movement in a single plane, like a hinge.
   • A joint of a finger when the fist is closed: Specifically refers to any of the joints where the fingers bend, particularly the prominent ones visible when a hand is clenched into a fist.

Usage Examples

• Noun (Anatomical):
  • He bruised his knuckle joint while boxing.
  • Arthritis can cause pain and swelling in the knuckle joints.
• Noun (Mechanical):
  • The robot's arm utilizes a knuckle joint for precise, hinged movement.
  • The design incorporates a durable knuckle joint to connect the two levers.

Advanced Usage

• "To rap someone's knuckles": To reprimand or punish someone lightly. (This idiom refers to the anatomical knuckle joint).
  • The teacher rapped his knuckles for talking in class.
• In mechanical contexts, a knuckle joint is a specific type of pin connection designed to handle tensile loads while allowing a pivoting motion.

Variants and Related Words

• Knuckle (n): The rounded prominence of a bone, especially at a finger joint; or the part of a hinge through which the pin passes.
  • He cracked his knuckles.
• Knuckled (adj): Having knuckles.
  • His large, knuckled hands.
• Knucklebone (n): A bone forming or corresponding to a knuckle.

Synonyms

• Finger joint (for the anatomical meaning).
• Hinge joint (for the mechanical meaning).
• Metacarpophalangeal joint (MCP joint) (technical term for the major knuckle joint connecting the hand to the fingers).

Related Phrases

• Knuckle down: To begin to work hard and seriously.
  • You need to knuckle down and study for your exams.
• Knuckle under: To submit or yield to authority or pressure.
  • After a long argument, he finally knuckled under.

Related Idioms

• White-knuckle: Describing a very frightening or tense experience, from the idea of gripping so hard one's knuckles turn white.
  • It was a white-knuckle ride on the roller coaster.
• Near the knuckle (BrE): Risqué or verging on the indecent or offensive.
  • Some of his jokes were a bit near the knuckle.

Noun

1. a joint allowing movement in one plane only
2. a joint of a finger when the fist is closed