Other forms: darning, darned
To darn a sock is to sew a hole shut by weaving thread across it, over and under, until the gap becomes fabric again. A wooden mushroom pushed into the heel to hold the shape, a long blunt needle, and twenty patient minutes.
The noun is the mended patch itself: a neat darn in the elbow of a jumper. Darning belongs to the world of mending rather than replacing, and a darning needle is thicker and blunter than a sewing one. The word then has a second life with nothing to do with cloth — darn is the polite stand-in for damn. Darn it, a darn good meal, well, I'll be darned. That one is mild enough to say in front of anybody, and you will meet it far more than the needle.
1verbdarnTo mend a hole in cloth or knitting by weaving thread back and forth across the gap.
“She sat by the window darning socks with grey wool.”
synonyms: mend
2nounwovenThe woven patch left where a hole has been mended.
“There is a darn on the knee, but you can hardly see it.”
3interjectionmildA mild substitute for 'damn', used to show annoyance.
“Darn, the shop closed five minutes ago.”
4adjectivenounUsed before a noun for emphasis, in place of 'damned'.
“That was a darn good film.”
The exclamation darn is what is called a minced oath: damn with the teeth filed off, changed just enough that it could be said in company without counting as swearing. English is full of these polite disguises, and darn is one of the oldest still in daily use.
A minced oath of damn.
Etymology from Wiktionary, CC BY-SA
Practised in Repair & Damage, Knitting & Sewing