Use of caps for zip code

I would like to know which of "ZIP Code" or "ZIP code" is correct. One of our contributors has alerted me to the fact that the term is a registered name owned by the US Postal Service, but, to my mind, it has become a generic term over time. What is the majority view?

Solution 1:

I checked a few standard U.S. style guides from the past to see how they handled the term ZIP/Zip/zip Code/code. In discussing the two-letter abbreviations of the various states, Words Into Type, Third Edition (1974) cites "the ZIP (Zone Improvement Program) code" for each abbreviation.

In contrast, Merriam-Webster's Ninth Collegiate Dictionary (1983) has this entry:

zip code n, often cap Z&I&P [zone improvement plan] (1963) a number that identifies each postal delivery area in the U.S.

The Chicago Manual of Style, Fourteenth Edition (1993) observes that "the two-letter form [of state abbreviations] is specified by the United States government for use with zip code addresses in mailing."

Perhaps the most baffling element here is the failure to agree on what zip stands for. A colloquy between Senator Absalom Robertson of Virginia and a Mr. McMillan of the Post Office Department during a hearing on appropriations for the next fiscal year seems dispositive [snippet]:

Senator ROBERTSON. Do I understand that "ZIP" stands for zone improvement program?

Mr. McMILLAN. Yes, sir, zone improvement program.

Various official government publications from the mid-1960s support this understanding of the name—but an approximately equal number of contemporaneous government publications identify ZIP as being short for "Zone Improvement Plan." Not surprisingly, the confusion trickled down to the private sector. The March 1968 issue of Changing Times ("The Kiplinger Service for Families") has this item:

Zip. Those five code numbers are very important to the delivery of your mail. So make an effort to use them. The zip (Zone Improvement Plan) system expedites handling and reduces errors, helping you and the post office.

But four months later, in discussing the Post Office's cartoon mascot Mr. ZIP, Changing Times included this note:

At first the figure was called "Mr. P.O. Zone." But the name was soon changed to "Mr. ZIP." (ZIP stands for Zone Improvement Program.)

An Ngram graph based on Google Search results for the past 50 years suggests that for most of that time, "Zone Improvement Plan" has been significantly more popular than "Zone Improvement Program." But considering how unsure the government itself seems to have been as to what the acronym zip stood for, it is hardly surprising that Merriam-Webster's (for one) would be inclined to identify "zone improvement plan" as a lowercase description rather than as an initial-capped official name. Nor is it surprising, given the Postal Service's emphasis on the swiftness of mail delivery that was sure to ensue following adoption of the new five-number codes, that ZIP itself became popularly understood not as an acronym at all but as a (lowercase) descriptive term.

Currently, Merriam-Webster's and Chicago favor "zip code," while the AP Stylebook continues to prefer "ZIP code"; none of these references capitalizes the c in code.

Solution 2:

This is another of those cases where opinions and style guides vary, and the writer should strive above all for consistency.

As elsewhere noted, ZIP Code is a U.S. Postal Service trademark, and originates with the Zone Improvement Plan. This is the orthography still preferred by the USPS, as indicated in its official mailing guidelines, as used throughout its website, and as found in official accounts such as The Untold Story of the ZIP Code. The expanded program is known as ZIP+4 or ZIP Code+4— though addresses using it are described as ZIP+4-coded.

The legal genericization or lack thereof of ZIP Code, I think, is irrelevant. ZIP Code is the original and arguably most accurate form, but such things change over time. Many argue for Web site over website, since it is not just any web, but the World Wide Web, yet even the Associated Press finally threw in the towel on that one not long ago; the all-lowercase single word website is prevalent.

FWIW, the 2008 U.S. Government Printing Office style guide lists ZIP Code as its preferred capitalization. But the GPO does not dictate style for anyone outside the GPO, even other agencies of the federal government. AP and the HHS website, among others, call for all-caps ZIP but lowercase code. The University of California, Berkeley style guide stipulates lowercase zip code.

As it happens, Google Books shows zip code far outpolling ZIP Code, ZIP code, Zip code, and zipcode by a good measure even in the early days of the program.

(As a low-incidence term, the unusual spikes may result from quirks in the volumes represented in Google Books; for example, they could reflect a change in a government style guide, and government documents might be overrepresented for recent decades.)