Who is an istenis? TB Yoma 34

Daf Yoma 34 finishes the discussion of the High Priest’s first immersion. The rabbis understood human nature and made allowances. “The mishna continues: If the High Priest was old or istenis (אִיסְטְנִיס), they would heat hot water for him on Yom Kippur eve and place it into the cold water of the ritual bath in order to temper its chill It was taught in a baraita that Rabbi Yehuda said: They would heat blocks of iron on Yom Kippur eve and cast them into the cold water of the ritual bath to temper its chill” (Sefaria.org translation)

I don’t know why the older we become the colder we feel, but I recognize this phenomena. That’s why many retirees moved to warmer climates like Florida. They just can’t tolerate the cold northern winters anymore. How many times have we seen the elderly wear sweaters on what younger people will call a very hot day! So too did the rabbis understand that older High Priests couldn’t tolerate a cold water mikvah; consequently, the heated the mikvah waters.

Istenis (אִיסְטְנִיס) obviously is a borrowed Greek word. My Alcalay Hebrew-English dictionary defines it as delicate, sensitive, fastidious, and refined. The Talmud describes an istenis as one who could not eat a lot (TB Pesakhim 108a), one who can’t tolerate seeing anything gross (Arukh, Rashbam on TB Baba Batra 145b ד"ה  זה איסתניס), and one who needs to wash more than the average person (TB Berakhot 104a-105a)

If the High Priest refused to answer a call mikvah because he was an istenis, then he could perform the appropriate rituals for Israel attaining atonement on Yom Kippur. That would be an intolerable situation; consequently, just like an elderly high priest they would warm up the mikvah waters for the High Priest who was an istenis.