lasting for only a very short time
Origin and usage
The adjective momentary comes from the Latin ‘momentarius’ which was derived from the noun ‘momentum’ meaning ‘moment’. It was first used in English in the late 15th century.
Something that is momentary lasts for a very short time, no more than a few seconds. The adjective momentary collocates with nouns like ‘lapse’, ‘pause’ and ‘lull’, as well as ‘distraction’, ‘interruption’, ‘inattention’ and ‘panic’. A momentary glimpse of something is just long enough to ascertain what it is you are looking at.
The related adverb momentarily is used in both British and American English, and means ‘for a moment’. It is often used with verbs like ‘pause’ and with adjectives like ‘stunned’, ‘distracted’ and ‘startled’. There is another meaning of momentarily, however, that is used mainly in American English. This one means ‘very soon’, generally comes at the end of a sentence, and is used in contexts such as ‘I’ll come back to these findings momentarily‘ or ‘The doctor will be with you momentarily‘.
“Scientific thought, then, is not momentary; it is not a static instance; it is a process.”
brief, fleeting, passing