The definition of installment is the act of putting something new in, or an installment is one part of something that has multiple parts such as a payment or story.
(noun)See installment in Webster's New World College Dictionary
noun
Origin: altered (infl. by install) < estallment < estall, to arrange payments for < OFr estaler, to stop, fix < estal, a halt, place < OHG stal: see stall
noun
Origin: install + -ment
See installment in American Heritage Dictionary 4
also in·stal·ment
nounOrigin:
Origin: Alteration of obsolete estallment
Origin: , from Anglo-Norman
Origin: , from Old French estaler, to place, fix
Origin: , from estal, place
Origin: , of Germanic origin; see stel- in Indo-European roots
.Learn more about installment