Jund-ul-Islam is an Arabic term that roughly translates to "armed Islamic forces." When talking about synonyms for this term, a few words come to mind. Firstly, "Mujahideen" refers to Islamic fighters who engage in physical combat in the name of their religion. Similarly, "Islamist militants" or "Islamic fighters" can also be used interchangeably with Jund-ul-Islam. Another popular term is "jihadists," which refers to individuals who believe in engaging in jihad (holy war) to defend and spread their religion. "Extremists" or "radicals" can also be used to describe these groups, although it's important to note that not all Muslim extremists are violent.