Sorry Panama pill, but this one is smaller. Travancore 1 chuckram. This thing is truly tiny, about the size of the head of a screw or nail. The package it came in had the date as 1860-1901 but I haven't yet checked on the accuracy of that. Here's a photo of the coin and then compared to a dime.
It is as you described, Travancore #KM21. It is silver, BTW. Nice pickup! I could see how a coin like that would easily get lost, much like our 3-cent silver coins (holes in pockets, dropped, etc.)
My smallest coin is also Travancore, they obviously have a thing about tiddlers. 1 cash, 11.3 mm, 0.48g, KM#57.
The shocking sizes of money throughout the ages never fails to amaze me. My two smallest coins include a James I half penny (1607 - 1609) and a Pisidia Selge Obol (250 - 190 BCE). Both measure somewhere around 10mm.