'assemblance' originates from Middle English, from Old French 'assemblance' (also spelled 'asemblance'), ultimately related to the verb 'assembler' meaning 'to bring together' or 'to assemble.'

'assemblance' appeared in Middle English as 'assemblance' (and variant spellings) influenced by Old French; over time the form persisted in literary and legal contexts but became rare in everyday modern English.

Originally associated with the idea of 'bringing together' or an act/instance of assembling (and by extension a group), the word's sense shifted toward 'outward appearance' or 'semblance,' and today it is mainly encountered as an archaic or literary synonym of 'semblance.'