prop
搘 centers on supporting or propping something up, typically with a physical object or effort.
搘 combines 扌 (hand) with 耆, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a hand action related to propping or supporting.
The hand radical 扌 beside 耆 suggests using your hand to prop something up, like a support beam.
For シ, imagine propping up a sheet of paper with your hand: sheet -> シ, and the hand supports it.