Momentarily means for a moment only — or, in American English, in a moment's time. The two meanings are genuinely different.
British English keeps the first, so pausing momentarily means pausing briefly. American English has largely moved to the second, so we will be landing momentarily means shortly. That difference has confused a great many passengers, since one version promises a landing soon and the other promises a very short one. Careful writers avoid the word altogether and say briefly or shortly instead.
1adverbmomentarilyFor a very short time.
“He hesitated momentarily before answering.”
2adverbuseIn a moment, chiefly in American use.
“The doctor will be with you momentarily.”
Latin
mōmentārius — of brief duration
Middle English
momentare
English
momentary
English, today
momentarily
Built from
From momentary + -ly. momentary comes from Middle English momentare, from Latin mōmentārius (“of brief duration”), from mōmentum (“a short time, an instant”). by surface analysis, moment + -ary.
Etymology from Wiktionary, CC BY-SA