installment (n.) Look up installment at Dictionary.com
"act of installing," 1580s, from install + -ment. Meaning "arrangement of payment by fixed portions at fixed times" is from 1732, alteration of Anglo-French estaler "fix payments," from Old French estal "fixed position, place," from a Germanic source akin to Old High German stal "standing place" (see stall (n.1)). Figurative sense of "part of a whole produced in advance of the rest" is from 1823.