'belong' originates from Middle English, specifically the word 'belongen' composed of the prefix 'be-' plus a verb 'longen' meaning 'to relate' or 'to have relation to'.

'belong' changed from the Middle English word 'belongen' (itself from be- + longen) and eventually became the modern English 'belong' and its past forms (e.g. 'belonged').

Initially, it meant 'to have relation or relevance to' or 'to pertain'; over time it evolved to include 'to be the property of' and 'to be a member of/fit in', which are the primary modern senses.