Enough O deed impromptu and secret, Enough O gliding present—enough O summ’d-up past.
…and the sullen remnant retreating, Till after midnight glimmer upon us the lights of a dim-lighted building, We come to an open space in the woods, and halt by the dim-lighted building, ’tis a large old church at the crossing roads, now an impromptu hospital, Entering but for a minute I see a sight beyond all the pictures and poems ever made, Shadows of deepest, deepest black, just lit by moving candles and lamps, And by one great pitchy torch stationary with wild red flame and clouds…
There are no more uses of "impromptu" in the book.
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In one picture, which seems like the most recent but still looks a few years dated, his dad has his arms around the two boys, and he’s squeezing them together for an impromptu photo.
Colleen Hoover -- Slammed
I hesitate for a split second, long enough to place the tune—Frank Sinatra, "New York, New York"—and say a prayer of thanks that the Pugs aren’t witness to my mom’s impromptu performance.