See under zip code.
Definition for initial code (2 of 2)
or ZIP code, Zip code
a system used in the U.S. to facilitate the delivery of mail, consisting of a five- or nine-digit code printed directly after the address, the first five digits (initial code) indicating the state and post office or postal zone, the last four (expanded code) the box section or number, portion of a rural route, building, or other specific delivery location.
Origin of zip code
1960–65, Americanism; Z(one) I(mprovement) P(rogram)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for initial code
the US equivalent of postcode
Word Origin for zip code
C20: from z (one) i (mprovement) p (lan)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012