To pay by instalments.
To connect, set up or prepare something for use, often specifically (in Computing) to transfer software onto a device's permanent storage and put it in a state where it is ready to be run when needed, usually decompressing it if necessary and performing any necessary pre-first-run configuration.
To admit formally into an office, rank or position.
To establish or settle in.
An installation. (Usage originated as a truncated form of the word installation.)
Installer. A software utility that installs an application.