This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
紣 combines 糸 (thread) with 卆, but the historical origin and original meaning are uncertain. It may be a variant or simplified form of another character, but the exact development is unclear.
The left side is thread 糸, and the right side 卆 looks like a tangled knot. Picture a thread tangled into a knot, but its meaning remains a mystery.
For サイ, imagine a sigh of frustration as you try to untangle the knotted thread: sigh -> サイ.
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