Swish-tail

One of the five ponies belonging to Meriadoc Brandybuck that he and his fellow adventurers took with them when they set out from the Shire for Rivendell. After a dangerous journey through the Old Forest, they came to the house of Tom Bombadil, where the five ponies were stabled with Fatty Lumpkin, Tom's own pony.

If Merry had given any of his ponies names at all, there is no record of them. 'Swish-tail' was a name given by Tom, as the Hobbits learned when he later rescued them in the Barrow-downs, calling their lost ponies by their new names. Swish-tail and its companions travelled as far east as Bree, but bolted from the inn stables there before the Hobbits could continue further. All five ponies eventually found their way back to Tom Bombadil and Fatty Lumpkin, who ultimately returned them to Barliman Butterbur, the innkeeper from whose stables they had been lost.