[in.stall.ment] also in.stal.ment n (1589): installation 1
[2]installment also instalment n [alter. of earlier estallment payment by installment, deriv. of OF estaler to place, fix, fr. estal place, of Gmc origin; akin to OHG stal place, stall] (1776) 1: one of the parts into which a debt is divided when payment is made at intervals
2. a: one of several parts (as of a publication) presented at intervals b: one part of a serial story -- installment adj