'mourner' originates from Old English, specifically the verb 'murnan' (also seen as 'murnian'), where the root 'murn-' meant 'to grieve' or 'to be sorrowful.'

'mourner' developed from Old English 'murnan' which passed into Middle English as 'mournen' or 'murnen'; the agentive suffix -er was added in Middle English to form 'mourner', giving the modern English word.

Initially connected to the action 'to grieve' (the verb); over time the derived agent noun came to mean 'a person who grieves or expresses sorrow,' especially at funerals.