Why is it der Moslem?

Moslem ends in -em. Most nouns with this ending are neuter (92% take das), but Moslem is an exception: der Moslem.

The other -em exceptions
Sense 1
der

Meaning

[1] Religion, Islam: supporters of Islamic faith

[1] Religion, Islam: Anhänger des islamischen Glaubens

Examples

[1] A Muslim is a member of the Islama

[1] Ein Moslem ist ein Angehöriger des Islam.

[1] "Before our departure, Endi Effendi quickly became Muslim" "

[1] „Vor unserer Abreise aber wurde Endi Effendi noch schnell Moslem.“
More source examples (1)

These dictionary examples can include historical and less common uses.

[1] "Apparently they were Moslemsä"

[1] „Offenbar waren sie Moslems.“

Declension

1 Singular Plural
Nominativ der Moslem die Moslems
Genitiv des Moslems der Moslems
Dativ dem Moslem den Moslems
Akkusativ den Moslem die Moslems

Pronunciation

Dictionary entries include material from Wiktionary. Wiktionary