male nettle-hemp
枲 refers specifically to the male plant of the nettle-hemp, a fiber plant. The meaning is narrow and botanical, without broader abstract extensions.
枲 is a phono-semantic compound: 木 (tree/plant) provides the meaning, and 台 likely contributes the sound. The character was created to name the male nettle-hemp plant.
The top 台 looks like a platform, and the bottom 木 is a tree or plant. Imagine a special platform where only male nettle-hemp plants are grown.
For シ, picture a single male nettle-hemp plant standing alone on the platform: she -> シ, and she is the only one there.