'appertain' originates from Old French 'apertenir' (also Middle English 'apperteinen'), ultimately from Latin 'pertinēre', where the prefix 'ad-' (rendered as a- in Old French formation) meant 'to' or 'toward' and 'tenēre' meant 'to hold'.

'appertain' changed from Middle English 'apperteinen' (influenced by Old French 'apertenir') and eventually became the modern English word 'appertain'; the past forms (such as 'appertained') follow regular English past-tense formation.

Initially it meant 'to hold toward' or 'to reach/relate to' (i.e., to concern or belong to), and over time this developed into the current meaning 'to belong to or be relevant to'.