I don't think there's a good answer. It's a loanword from Sumerian (maybe through Akkadian/Aramaic) with a unique look. The Academia of Hebrew Language commented in the past:The word "throne" is כסא kissee. Why does it become כסאי kis'i and כסאו kis'o when a pronoun is attached? Is there a rule for it?
A historical short i. If you're talking about כסא kissē, then historically it was (and perhaps only hypothetically) kissi’. If you're talking about אויב ’ōyēv, then historically it was ’āyib.Ali Smith: You claim that a short i goes to a שווא rather than to a צירי in pretonic position when the propretonic syllable can't be changed, either because it (the propretonic syllable) is a closed syllable or is historically long.
Where is the short "i" in this word?