Wiktionary
vb. To prepare a horse for riding by equipping it with tack (harness, reins, saddle etc.)
Usage examples of "tack up".
About once a month Lavadie had to tack up a fresh sign because the old one, perforated by bullet holes, became illegible--Lavadie's gravel pit also happening to be the place to sight in one's rifle during the several months preceding deer season, during which time Lavadie didn't even bother to replace his sign lest somebody decide to adjust his crosshairs against the bridge of Lavadie's nose, or across the third brass button from the top of his vest, which was situated more or less directly over his heart.
That was a signal to the stable hands to tack up that particular Companion, and if everyone got the timing right, the Companion would meet his Chosen at the entrance to the stable, all ready to go.
And the way that wind blows down the canyon, any attacking rafts would have the devil of a time trying to tack up-canyon against them while carryin' on a runnin' fight.
Where he observed his daughter, Maria Blandina, teetering on the top of a too-short step stool, trying to tack up a new set of alphabet letters.
Uncle Monty had allowed her to tack up large pieces of white paper on each wall, so she could sketch out her ideas, even if they came to her in the middle of the night.
The last Act demands that you tack up your notice for thwee Sundays in August or September.
Yet I had always to turn again and tack up in the wind's eye, for it was not merely a height record that I was after.
He took the thumbtacks, then with a quick look around to make sure he was unobserved, he used them to tack up the notice right over the crack where the main doors came together.