The capital of Jordan, called 3ammaan, is also spelt the same way, but with a different vowel diacritic on the first letter: عَمَّان. I'm used to pronouncing the name of the country with only one m, 3umaan, not 3ummaan, personally, so this was confusing even to me.
Not only is it distinguished by the diacritic on the 3ayn "ع", but also by the gemination on the "م".
عمان vs. عمّان
3ummaan is wrong as it is pronounced. There's no stressing on the "m" when saying عُمان..