(n.) a late-summer flash of lightning
When the heat of the late summer sparks thunderstorms, you might spot a hairst-blink—a late-summer flash of lightning.
As you might be able to tell from the spelling of that word, this is a term from Scots. Etymologically, blink is simple enough—but hairst?
It is a dialect corruption of harvest, recorded in Scots literature since the early 1700s, but presumably in use much earlier than that date would suggest. It crops up in a delightful array of Scots expressions, including hairst fee (a wage paid to a harvest worker), hairst knot (a loop of harvest straw used as a decoration for the horses), hairst Monday (the Monday four weeks before the harvest begins), and hairst play (school holidays during the harvest autumn period). And, according to the Scottish National Dictionary, in the dialects of the far north of Scotland in particular, in the expression hairst-blink.