'island-related' originates from Modern English, specifically the compound of 'island' and 'related', where 'island' meant 'land surrounded by water' and 'related' comes from 'relate' meaning 'connected'.

'island' changed from Old English 'īegland' (also spelled 'iegland') and eventually became the modern English 'island'. 'Related' is the past participle/adjectival form of 'relate', which came into English via Old French from Latin 'relatus' (past participle of 'referre'). These elements combined in modern English to form the compound adjective 'island-related'.

Initially the components meant 'land surrounded by water' and 'connected/related'; over time they combined into the compound meaning 'connected to or concerning islands'.