A coat with tails; specifically, a coat with a divided skirt cut away in front, like a dress-coat, or the so-called swallow-tailed coat. (noun)
The Century Dictionary (Public Domain)
Use "tail-coat" in a sentence
"AzuraTheBlueDevil didn't think so: "I turned up for the school run in a tail-coat and knee-highbuckle-up pirate boots the otherday.""
"He does not assume the tail-coat and the manners of manhood too early: he holds his tongue, and listens to his elders: his mind blushes as well as his cheeks: he does not know how to make bows and pay compliments like the young Frenchman: nor to contradict his seniors as I am informed"
"In part it was a modest cancan, in part a step dance, in part a skirt-dance (so far as my tail-coat permitted), and in part original."