'pertain' originates from Latin, specifically the word 'pertinere', where 'per-' meant 'through' or 'completely' and 'tenere' meant 'to hold'.

'pertain' changed from Medieval/Old French forms like 'pertener' and Middle English 'perteinen', and eventually became the modern English word 'pertain' via these Middle English forms.

Initially it meant 'to reach to, to extend to' or 'to hold toward/with', and over time it evolved into the current sense 'to relate to or be relevant to'.