When did "regular" start referring to Type 3 languages/grammars?
I found an answer, at least a partial one, hinted at in Footnote 10 of Chomsky's paper where he refers to a 1956 paper by Kleene in which Kleene describes &quot;regular events&quot; -- a language recognized by finite state machines.
So it would seem the common usage of &quot;regular language&quot; today traces back to Kleene's &quot;regular events&quot; rather than to Chomsky's &quot;regular grammar&quot;.
Furthermore, as renierpost pointed out in a comment, what Chomsky called a &quot;regular&quot; grammar in 1959 is now known as Chomsky normal form.
Edit: I asked Professor Chomsky via email whether he intended his &quot;regular grammar&quot; to have a connection to Kleene's &quot;regular events&quot;. He replied: &quot;Long time ago and I don't recall. I suppose just a coincidence.&quot;