Definition of "afoot"

"The dogs were no sooner let loose, than the hare was afoot.

1886, Peter Christen Asbjørnsen, translated by H.L. Brækstad, Folk and Fairy Tales, page 77

Hamlet: […] I prithee, when thou seest that act afoot, / Even with the very comment of thy soul / Observe mine uncle: […]

c. 1599–1602 (date written), William Shakespeare, “The Tragedie of Hamlet, Prince of Denmarke”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act III, scene ii]

Possibly some chemical experiment was afoot; possibly----Well, it was no business of mine to speculate upon why he wanted it.

1913, Arthur Conan Doyle, “(please specify the page)”, in The Poison Belt […], London; New York, N.Y.: Hodder and Stoughton

In San Francisco and in New Jersey, to quote two other examples, plans are afoot to subsidise new commuter line construction or existing operations out of toll revenue from state highways or bridges.

1959 October, “Talking of Trains: Paying for the commuters”, in Trains Illustrated, page 458

‘Patience,’ said Slartibartfast again. ‘Great things are afoot.’¶ ‘That's what you said last time we met,’ said Arthur.¶ ‘They were,’ said Slartibartfast.¶ ‘Yes, that's true,’ admitted Arthur.¶ All, however, that seemed to be afoot was a ceremony of some kind.

1982 August, Douglas Adams, Life, the Universe and Everything (The Hitchhiker’s Guide to the Galaxy; 3), London: Pan Books, page 29

Sunny moves through these final days quickly, easily, buoyed by routine even though change is afoot in all directions.

2011, Maile Chapman, Your Presence Is Requested at Suvanto: A Novel‎

Now there are plans afoot to introduce a couple of extra trains to the timetable in December, with the long-term goal of a doubling of the service to eight trains a day.

2019 October, James Abbott, “Esk Valley revival”, in Modern Railways, page 76