Irumu - Irumu

Japanese: イルム - いるむ

...In other words, Islam, which referred to faith in general, became al-Islām, a religion with specific faith content, and at the same time, Muslim was established as a name to refer to believers, a name that has remained to this day.
[The Establishment of Theology and Jurisprudence]
The Arabic words for knowledge are 'ilm, fiqh, ma'rifa, and hikma. 'ilm originally meant knowledge acquired through effort, and therefore knowledge of the Quran and hadith (traditions about the words and deeds of the Prophet Muhammad), that is, theological knowledge, was called 'ilm.

From [Ulama]

...The singular form is 'ālim. The word 'ulama refers to people with 'ilm (knowledge), but here 'ilm is used in the sense of religious knowledge, not knowledge in general. Thus, 'ulama refers to scholars of religious sciences, and does not include scholars of so-called ancient sciences such as philosophy and mathematics.

*Some of the terminology explanations that mention "Ilum" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…すなわち信仰一般を指すイスラームislāmは特定の信仰内容をもつ宗教イスラムal‐Islāmになったのであり，同時に信者を呼ぶ名としてのムスリムも確立し，その後現在にまでいたっている。
［神学と法学の成立］
　知識を意味するアラビア語にイルム‘ilm，フィクフfiqh，マーリファma‘rifa，ヒクマḥikmaがある。イルムは元来，努力によって習得される知識を意味し，したがってコーランやハディース(預言者ムハンマドの言行に関する伝承)に関する知識，すなわち神学的知識をイルムといった。…