肼 is a chemistry-domain character - the Chinese name for hydrazine, a colorless flammable liquid (NH2-NH2) used in rocket propellants and pharmaceuticals. The character was coined in modern times for this compound; it has no other common usage.
memory
Radical 月 (flesh/organ, common in body/biological terms) + phonetic 井 (jǐng, 'well'). The 井 gives both shape and sound - picture a chemistry well of toxic liquid.
⺼ is the flesh radical, recycled here as a "body/biology" marker for organic chemistry - Chinese chemical names often borrow ⺼ for nitrogen-bearing compounds. Same trick in 胺 amine, 肽 peptide. Modern coinage, not classical etymology.
井 supplies the sound jǐng exactly, same tone - a pure phonetic borrowing for the chemistry term hydrazine (N₂H₄). The picture of a well has no semantic role here.
