hoe, mattock
鎡 centers on a heavy digging or chopping tool: a hoe or mattock used for breaking ground.
鎡 combines 金 (metal) with 兹, which likely contributes the sound. The character refers to a metal farming tool such as a hoe or mattock.
The left side is metal 金, and the right side 兹 looks like a tangled field. Picture a metal hoe cutting through the tangled growth.
For シ, imagine a shiny metal hoe: the 'shi' sound of 'shiny' cues シ while the metal blade digs into the earth.