Wiktionary
vb. (context architecture English) To fasten by one of the ends into a wall or some other support.
Usage examples of "tail in".
The Steed was so impressed and excited at being presented to the Ruler of all Oz that he scarcely knew what he was doing, and managed to knock over two footstools, and then stand for some moments with his tail in a bowl of flowers and one hoof solidly on Queen Farthingale's train, until Fess moved him and released her.
I mean size does count, and a girl could get some respect with a boyfriend like you, if you had a tail in proportion.
He began to make rapidly for the yacht, beating the waves violently with his fins, and keeping his tail in a perfectly straight line.
But once he understood that Charlie meant it and would not be swayed, he trotted back, tail in air, and supervised campmaking.
If you look carefully, you can see where it dragged its tail in the dirt.
He put the dirty plate in the dishwasher, swabbed off the sink, and went out, leaving Rachel to deal with the cat that had jumped onto her lap and dipped its tail in her coffee.
So Topthor and the rest of his miserable fleet had turned tail in order to save their skin!
Though Henry might occasionally fan his tail in my direction, it is understood that he is loyal to only one person, which, I think, is another reason my sister is so fond of him.