'Marian-related' is formed in modern English by combining 'Marian' (from Latin 'Marianus', derived from 'Maria', meaning 'of Mary') and 'related' (from Late Latin 'relatus', the past participle of 'referre', via Old French and Middle English, meaning 'brought back' / 'related').

'Marian' changed from Medieval Latin 'Marianus' (meaning 'of Maria') into Middle English as 'Marian' and retained its adjectival sense; 'related' evolved from Late Latin 'relatus' to Old French 'relater' and Middle English 'relaten', eventually becoming the modern English past-participle/adjective 'related'.

Initially, 'Marian' meant 'belonging to Maria/Mary' and has largely retained that sense in religious and proper-name uses; 'related' originally had a sense tied to 'carried back' or 'recounted' and shifted to the broader modern sense of 'connected' or 'having a relation'.