This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
穝 is a rare character composed of 禾 (grain) and 最 (most). The exact historical development is uncertain, and it may be a variant or a character with limited usage.
With no clear meaning, picture a rare grain stalk (禾) that is the most (最) unusual in the field, but its purpose remains a mystery.
For サイ, imagine a sigh (サイ) of frustration when you cannot figure out what this rare grain kanji means: sigh -> サイ.
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