'appearance-based' is a compound formed from 'appearance' and the participial adjective-forming '-based'. 'appearance' originates from Old French 'aparence' (from Latin 'apparēre'), where the Latin root meant 'to appear, become visible'. The element '-based' comes from English 'base', ultimately from Late Latin/Greek 'basis' meaning 'foundation'.

'appearance' came into Middle English from Old French 'aparence' and earlier Latin 'apparēre'; over time it established the modern form 'appearance'. 'base' entered English via Old French and Middle English from Late Latin/Greek 'basis', and '-based' developed in modern English to form compounds meaning 'having as a basis'. The compound 'appearance-based' is a recent formation using this pattern.

Initially 'appearance' referred to the act or fact of appearing (coming into view); over time it narrowed to often mean the outward look or visible aspect. 'Base' originally meant a foundation; '-based' evolved to mean 'rooted in' or 'determined by', so 'appearance-based' now means 'rooted in or determined by appearance'.