Mussulman

Mussulman is an old form of Muslim.

Mussulman is not formed from the English 'man', but is either Arabic or Persian, and may be formed from the Arabic muslimūn ('those who have converted to Islam, Muslims'), a participle from the verb aslama ('to convert to Islam'). You are recommended not to use Mussulman, as it was often used dismissively and slightingly in the days of the British Empire, and is, consequently, now felt to be insulting by many of the people it is used to label.

If you should stray into using it, note that the preferred plural is mussulmans, not mussulmen.