אבן עזרא — בית הסהר

Q — "בית הסהר" appears uniquely in the Yosef narrative — is it Hebrew or an Egyptian loanword?

A — Ibn Ezra develops a precise philological diagnostic. The Torah follows "בית הסהר" with an explanation — "מקום אשר אסירי המלך אסורים." The Torah's self-explanation is the tell: it's an Egyptian loanword. He cross-references the exact same move in Megillat Esther — "האחשתרנים בני הרמכים" — where the Persian-loanword "אחשתרנים" is immediately glossed by the Persian-loanword "הרמכים" (horses, also a Persian word that Ibn Ezra explains). Two principles together: (1) Tanach uses local-language vocabulary appropriate to its setting — Egyptian in Egypt, Persian at the court of Achashverosh; (2) the very act of glossing a word identifies it as a loanword. The methodological move: Ibn Ezra turns the presence of an explanation into evidence about lexical origin.