Definition of "alertly"

Behind one of the old oaks which we have described in the preceding chapter, shrouding himself from observation like a hunter watching for his game, or an Indian for his enemy, but with different, very different purpose, Tyrrel lay on his breast near the Buck-stane, his eye on the horse-road which winded down the valley, and his ear alertly awake to every sound which mingled with the passing breeze, or with the ripple of the brook.

1823 December 23 (indicated as 1824), [Walter Scott], chapter 9, in St Ronan’s Well. […], volumes (please specify |volume=I to III), Edinburgh: […] [James Ballantyne and Co.] for Archibald Constable and Co.; London: Hurst, Robinson, and Co.

I walked fast to avoid being overtaken. Every crossing was a danger, every passenger a thing to watch alertly.

1897, H[erbert] G[eorge] Wells, chapter 23, in The Invisible Man: A Grotesque Romance, New York, N.Y., London: Harper & Brothers Publishers

Miss Baker and I exchanged a short glance consciously devoid of meaning. I was about to speak when she sat up alertly and said “Sh!” in a warning voice.

1925, F[rancis] Scott Fitzgerald, chapter 1, in The Great Gatsby, New York, N.Y.: Charles Scribner’s Sons, published 1953

She was wearing tight white shorts and a grey tank top of Jasper’s, in which her small breasts moved alertly.

2004, Alan Hollinghurst, The Line of Beauty […], 1st US edition, New York, N.Y.: Bloomsbury Publishing