When and how did "momentarily" come to mean "in a moment", rather than "for a moment"?

"Momentarily" used to mean "for a moment" only, and not "in a moment". Thus, newscasters could be divided into two clear groups: those who would say "we'll be back momentarily," and those who would not.

This restriction made sense to me, because having both definitions would promote ambiguity if a unique interpretation could not always be derived from the context. But in recent years it seems "momentarily" is regularly, maybe even more often, used to mean "in a moment" by newscasters of every caliber, and in fact this is even shown to be the definition when looked up in most dictionaries.

When did this word's meaning change? How did it come about?

Solution 1:

The Patrician, Lord Vetinari:
'I shall deal with the matter momentarily,' he said. It was a good word. It always made people hesitate. They were never quite sure whether he meant he'd deal with it now, or just deal with it briefly.
And no-one ever dared ask.

Guards! Guards! - Sir Terry Pratchett

Solution 2:

(answer copied over from this later question closed as a dup)

I think it's misleading to suggest the two different meaning are simply "the" American and British usages. I'm sure most competent speakers on both sides of the pond are perfectly well aware the word has both meanings (and has done for centuries).

It's true Brits normally use it to mean lasting for a moment, as opposed to Americans normally using it to mean about to happen in a moment. But we all transparently understand the other meaning when we encounter it - and context usually makes it abundantly clear which is intended. Only pedantic Americans would fret over "The display flickered momentarily", and I disown any of my fellow Brits who would take issue with "The dam will burst momentarily".

The good folk over at Merriam-Webster love taking side-swipes at such pedantry. They devote nearly a whole page to this one word in that link, and it seems to me every other paragraph takes a pop at anyone claiming it (or indeed any other word) can only have one meaning.

To summarise the MW position, a couple of centuries ago, momentarily had four meanings - instantly, from moment to moment, briefly, and very soon. The first two have long fallen into disuse. In the early 1900s that fourth meaning, which had hitherto been quite rare, gained traction in America by extension/conflation with the second meaning. Both the last two meanings are currently valid in the US and UK, but the fourth is relatively rare in current British usage.

Solution 3:

I just searched Google NGrams for the phrase "back momentarily"; the first appearance of the phrase seems to be around 1850, but the first appearance with the meaning in, rather than for, a moment appears to be in the History of the Fifteenth Regiment, New Hampshire Volunteers, 1862-1863 (published 1899):

While he was gone we received orders from headquarters, and our Lieutenant Pickering drew up the company, expecting the captain back momentarily.

In principle, I fully agree that this usage is incorrect... but I don't think we can blame anyone still living for it.

Solution 4:

Searching for "momentarily expecting" yields some very old uses with the meaning "in a moment".

From The Fast of St. Magdelen, by Anna Maria Porter, 1818, via Google books.

Momentarily expecting the appearance of this person, and winding up her spirit to sustain the rude encounter of probable insult or menace from him, she sat down on her bed, alternately listening to hear whether her enraged gaolers were coming, or ejaculating an agonized appeal to heaven.

And from 1744

... on the 4th we had 10 feet water in our hold, which made our condition very bad, and the dread of death appeared in every face, for we momentarily expected to be swallowed up;

There are lots of instances of "momentarily expect(s/ed/ing)" from the early 1800s with this meaning, so it's been used this way fairly regularly for at least 200 years. In fact, from the following Ngram, the phrase "momentarily expected" has been declining in use, which is very weak evidence for the word "momentarily" shifting in meaning away from the meaning "in a moment".

If you look at old dictionaries and grammars with Google books, you discover that some of them (for example, Chambers's, 1867) say that the word you were supposed to use for this sense of momentarily was momently, but from the above Ngram, it appears that momentarily has always been more popular than momently, even for this meaning.

If you look at Ngrams, you discover that momently was also used for both meanings in the early 1800s:

And from this chasm, with ceaseless turmoil seething,
As if this earth in fast thick pants were breathing,
A mighty fountain momently was forced; —Kubla Khan, Coleridge, 1797.

What I think may have happened was that in the early 1800s, there were two words, momentarily and momently, with essentially the same two meanings (either "in a moment" and "for a moment"). Some prescriptive dictionary writers decided to assign one meaning to momentarily and the other to momently, but it never caught on. To defend the dictionary writers, this difference in meaning is indeed justified etymologically, since momentarily is derived from momentary, meaning for a moment, while momently is derived directly from moment.

The word momently is now effectively gone from the English language, but prescriptive grammarians still say that momentarily should only have the one meaning.