installment

• instalment (Commonwealth)

• enPR: ĭn-stôlʹmənt, IPA^(key): /ɪnˈstɔːlmənt/

A 1732 alteration of estallment, from Anglo-Norman estaler (“fix payments”), from Old French estal (“fixed position”), from Old High German stal (“stall", "standing place”)

The sense of "part of a whole produced in advance of the rest" is from 1823.

installment (plural installments)

1. A portion of a debt, or sum of money, which is divided into portions that are made payable at different times. Payment by installment is payment by parts at different times, the amounts and times (often equal namely regular, e.g. mensual) being often definitely stipulated.
2. A part of a broadcast or published serial.
   • 2010, Michael A. Cramer, Medieval Fantasy as Performance, →ISBN, page ix:

     With The Two Towers, the new installment of the Lord of the Rings trilogy, about to storm the box office, we are seeing what might be called the enchanting of America.

   • 2012, Charles W. Chesnutt, The Marrow of Tradition, →ISBN:

     It is a serial story which we are all reading, and which grows in vital interest with each successive installment.

3. A part of anything that is performed in parts, spread over time.
   • 2009, Richard Leviton, Santa Fe Light: Touring the Visionary Geography of Santa Fe, New Mexico, →ISBN:

     Granted, this was but the first installment in the long process of “hatching” and mastering a dragon egg, but it was a good start.

   • 2014, Karen Lee-Thorp, A Compact Guide to the Christian Life, →ISBN:

     The blessings of the kingdom (healing, freedom, Stan's defat, abundant life, relationship with the King) are available now. Yet they are available only as a foretaste, the first installment of what will come when Christ returns.

   • 2015, How to Write About Music, →ISBN, page 193:

     Now bands like Mumford and the Lumineers are fulfilling that role, but they're also becoming the latest installment of the whole "indie goes mainstream"/"mainstream co-opt indie" thing that's been happening since Seth Cohen's heyday -- or, you know, since Don Draper married Megan.

For this sense in the UK, the OED permits only the spelling instalment. Commonwealth usage varies.

• (portion of a debt):
• (part of a broadcast or published serial): episode, part

From install +‎ -ment, install from Old French installer, from Medieval Latin installare, from Medieval Latin in- and Medieval Latin stallum, stall from a Germanic source (compare Old High German stal)

installment (plural installments)

1. The act of installing; installation.
   • (Can we date this quote?) John Milton

     Take oaths from all kings and magistrates at their installment, to do impartial justice by law.

   • 2000, Rebecca Neason, Guises of the Mind, →ISBN, page 183:

     In the twenty-two years Faellon had been Chief Servant, he had officiated at many royal ceremonies, including the burial of Joakal's father and mother, and Joakal's own installment as King nine years ago.

2. (obsolete) The seat in which one is placed.
   • (Can we date this quote?) William Shakespeare

     The several chairs of order, look, you scour; […] Each fair installment, coat, and several crest / With loyal blazon, evermore be blest.

• investiture, investment
• installation

• installment in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913.
• Webster's Seventh New Collegiate Dictionary, Springfield, Massachusetts, G.&C. Merriam Co., 1967
• “installment” in Douglas Harper, Online Etymology Dictionary, 2001–2019.