Where does “Mahommedanism” come from?

Mahommedanism (English) comes from English Mahommedan, from English Mohammedan, from English -an, from Italian -ana, from Spanish -ana, from Latin -ana, from Latin -anus, from Latin -um.

Ancestry of “Mahommedanism”, step by step

Mahommedanism traces back through two separate lines of ancestry.

via English Mahommedan

StepLanguageWordMeaning
1EnglishMahommedanAlternative form of Mohammedan
2EnglishMohammedanMuslim; Muslim, Islamic; relating to Mohammed
3English-anOf or pertaining to;
4Italian-ana-an, -y
5Spanish-anafeminine singular of -ano
6Latin-anainflection of -ānus: ## nominative/vocative...
7Latin-anusOf or pertaining to; -ian
8Latin-umnominative neuter singular of -us; accusative...
9Proto-Italic*-om
10Proto-Indo-European*-oHom

via English ism

StepLanguageWordMeaning
1EnglishismAn ideology, system of thought, or practice that...
2English-ismUsed to form nouns of action or process or result...
3Latin-ismus-ism
4Ancient Greek-ισμόςForms abstract nouns
5Ancient Greek-μόςForms abstract nouns
6Proto-Indo-European-mósCreates action/result nouns from verb stems
Every word from Proto-Indo-European *-oHomEvery word from Latin -anaEvery word from English -an