The first publication of this dictionary, also called
NI2 or
Webster's 2nd, came in 1934, but revised editions were issued over the next couple decades. This is (still) the largest dictionary of
American English ever published, with over
600,000 entries.
Of course, it did so at the expense of including words like sensifacient, a word which appeared in print once in the late 18th century, and polyphloesboean, also spelled polyphloisboian and poluphloisboian, etc. (It says etc. in the list of alternate spellings!), defined as "Loud-roaring; -- applied to the sea by Homer." (which of course suggests that it only appears in the English language as transliterations of the Greek word Homer used, in English translations of his works). As if those three spellings weren't enough, there are also three additional spellings of adjectives and two nouns derived from the word listed at the end of the definition. At least they discreetly chose not to list a cross-reference for the polu- spellings in their normal alphabetical position (three pages earlier), as they would have done for a more common word with alternate spellings located so far from alphabetical order.
At the time, the purpose of a dictionary was thought of as prescribing the
words and usage of those words that is considered standard, as opposed to
presenting language as it is actually used. Thus, well-known texts were
used as a basis for the dictionary, and in most cases, every word in these
texts was defined in the dictionary. (There were other ways that words
could enter the dictionary, but this provided the bulk of the obscure ones.)
It is for this reason that every word used in the works of Shakespeare
appears in NI2, even the names of the characters. NI2 was the end result
of more than 100 years of continually adding to the dictionary in this way,
going back to Noah Webster's original dictionary.
Note: Webster 1913 is based on the first edition of the New International Dictionary; specifically, on a revision of that dictionary printed in 1913. The NI2 dictionary is the next major revision of that work.
See also Fake words and broken definitions in dictionaries.