This tweet and this blog entry on the first use of the term "programming language" evoked responses from readers with some new history and some prior occurrences.

Doug Moen pointed me to the 1956 Fortran manual from IBM, Chapter 2 of which opens with:

Any programming language must provide for expressing numerical constants and variable quantities.

I was aware of the Fortran manual, which I link to in the notes for my compiler course, and its use of the term. But I had been linking to a document dated October 1957, and the file at fortran.com is dated October 15, 1956. That beats the January 1957 Newell and Shaw paper by a few months.

As Moen said in his email, "there must be earlier references, but it's hard to find original documents that are early enough."

The oldest candidate I have seen comes from @matt_dz. His tweet links to this 1976 Stanford tech report, "The Early Development of Programming Languages", co-authored by Knuth. On Page 26, it refers to work done by Arthur W. Burks in 1950:

In 1950, Burks sketched a so-called "Intermediate Programming Language" which was to be the step one notch above the Internal Program Language.

Unfortunately, though, this report's only passage from Burke refers to the new language as "Intermediate PL", which obscures the meaning of the 'P'. Furthermore, the title of Burke's paper uses "program" in the language's name:

Arthur W. Burks, "An intermediate program language as an aid in program synthesis", Engineering Research Institute, Report for Burroughs Adding Machine Company (Ann Arbor, Mich.: Univ. of Michigan, 1951), ii+15 pp.

The use of "program language" in this title is consistent with the terminology in Burks's previous work on an "Internal Program Language", to which Knuth et al. also refer.

Following up on the Stanford tech report, Douglas Moen found the book Mathematical Methods in Program Development, edited by Manfred Broy and Birgit Schieder. It includes a paper that attempts "to identify the first 'programming language', and the first use of that term". Here's a passage from Page 219, via Google Books:

There is not yet an indication of the term 'programming languages'. But around 1950 the term 'program' comes into wide use: 'The logic of programming electronic digital computers' (A. W. Burks 1950), 'Programme organization and initial orders for the EDSAC' (D. J. Wheeler 1950), 'A program composition technique' (H. B. Curry 1950), 'La conception du programme' (Corrado Bohm 1952), and finally 'Logical or non-mathematical programmes' (C. S. Strachey 1952).

And then, on Page 224, it comments specifically on Burks's work:

A. W. Burks ('An intermediate program language as an aid in program synthesis', 1951) was among the first to use the term program(ming) language.

The parenthetical in that phrase -- "the first to use the term program(ming) language" -- leads me to wonder if Burks may use "program language" rather than "programming language" in his 1951 paper.

Is it possible that Knuth et al. retrofitted the use of "programming language" onto Burks's language? Their report documents the early development of PL ideas, not the history of the term itself. The authors may have used a term that was in common parlance by 1976 even if Burks had not. I'd really like to find an original copy of Burks's 1951 ERI report to see if he ever uses "programming language" when talking about his Intermediate PL. Maybe after the holiday break...

In any case, the use of program language by Burks and others circa 1950 seems to be the bridge between use of the terms "program" and "language" independently and the use of "programming language" that soon became standard. If Burke and his group never used the new term for its intermediate PL, it's likely that someone else did between 1951 and release of the 1956 Fortran manual.

There is so much to learn. I'm glad that Crista Lopes tweeted her question on Sunday and that so many others have contributed to the answer!