knee, lap
膝 centers on the knee joint and the lap area formed when sitting. Both meanings describe the same part of the body from different angles.
膝 combines the flesh radical ⺼ with 桼, which likely provides the sound and may relate to the idea of a joint or bending. The exact historical development of 桼 is uncertain.
The left side ⺼ (flesh) marks a body part, and the right side 桼 looks like a person bending with a tree-like support. Picture the knee as the flesh part that bends like a hinge.
For シツ, imagine sitting on your knees in a quiet room: shitsu (しつ, room) -> シツ, and your knees are on the tatami.
knee
laying one's head in someone's lap; using someone's lap for a pillow
near one's knee
below the knee
kneecap; patella
beside a nobleman; close aid (of a nobleman, etc.)
to humbly implore; to beg profusely
both knees
knee replacement; knee arthroplasty; artificial knee joint replacement
gonarthrosis; osteoarthritis of the knee
knee
one knee
to kneel down on one knee; to genuflect
to sit on the floor with one knee raised; to raise one knee; to sit with one knee up
Japanese chaff flower (Achyranthes japonica)
knee touch down
sitting with one knee drawn up
to have one's knees be about to give way
two heads are better than one; consult even with your knees
kneecap