joint between bones; knuckle
Refers to the physical joint or knobby part of a bone, often where bones meet. Can be used for knuckles or other bony protrusions.
The cold makes the joints in my hands ache.
He cracked his knuckles.
Figurative use for strength of character, resilience, or determination. Often used in expressions like 骨っ節がある (to have backbone).
He is a man of backbone.
She has the grit to not give in to hardship.
Compound of 骨 (bone) and 節 (joint, node), with an emphatic geminate っ. The figurative sense likely developed from the idea of a strong physical backbone.