instalyoudaoicibaDictYouDict[instal 词源字典]
instal: [16] To instal someone was originally literally to put them ‘into a stall’. The word comes from medieval Latin installāre, a compound verb based on the noun stallum ‘stall’, and referred originally to the formal induction of someone into an office by ceremonially placing them in a seat or ‘stall’, such as the choir stall of a cathedral. The instalof instalment [18], incidentally, is a different word, although the two are ultimately related.

It is an alteration of an earlier estallment ‘arrangement for payment’, which came from Anglo-Norman estaler ‘fix payments’. This was a derivative of estal ‘fixed position’, which was borrowed from Old High German stal ‘place’ (source also of medieval Latin stallum).
=> instalment, stall[instal etymology, instal origin, 英语词源]