Install

The verb 'to install' is spelled thus in both British and American varieties of English. In both, the inflections also have a double '-l', installed in the past forms and installing in the present participle.

The related nouns are written

• installation, in both British and American English. This denotes a process, or the result of a process, such as
  • in traditional and formal terms, the process of naming or inducting a person into an official position, such as the Chancellor of a University, a Bishop into his cathedral or a knight into the Order;
  • in more modern and technical usage, the building, fitting or setting going of a piece of equipment or apparatus, such as an emergency power generator to guard against the failure of the electricity supply; an oil rig; or a computer program. Two more restricted meanings have become common:
    • in military circles, an installationis a base or facility, such as an anti-aircraft installation (a complex of different types of guns, missiles etc designed to protect a position against aerial attack), or a nuclear installation, which may contain the warheads, missiles, launch pad and associated teams of soldiers and their accommodation, etc, to launch a nuclear strike;
    • in the art world, an installation is a three-dimensional structure designed to be built. or assembled, in the specific spaces (such as a gallery or a museum) in which it is to be viewed, for example Carl Andre's 'Tate Bricks', a rectangular arrangement of 120 firebricks on the floor of the Tate Modern gallery in London.

• instalment in British English, and installment in American. (This difference can confuse those who see the word most often in connection with computer software that has been written, or described, in an area where American is the normal variety.) This denotes a part-payment, usually made at regular intervals, of a greater total of debt.
  • In American English, the phrase installment plan is commonly used to mean what in Britain was traditionally called hire purchase: buying large consumer goods, such as cars or refrigerators, for instant delivery, usually on payment of a deposit, with the remainder of the price being paid (with interest) over a period at intervals usually of a month or a week.

You may also want to see a note on the spelling pattern involved at -l - -ll-.