'Britain-lovers' is a modern English compound formed from 'Britain' + 'lover'. 'Britain' ultimately comes from Latin 'Britannia', and before that from Greek 'Prettanike' (Πρεττανική), reflecting a native Celtic name (reconstructed as *Pritani) for the islands. 'Lover' comes from Old English 'lufere' / the verb 'lufian' from Proto-Germanic *lubōną meaning 'to love'.

'Britain' entered English via Latin 'Britannia' (and Old French influence) and developed into Middle English 'Breteyne'/'Bretaigne' before stabilizing as 'Britain'. 'Lover' developed from Old English 'lufere' (one who loves) and the verb 'lufian', becoming the modern English 'lover'. The compound form (e.g. 'Britain-lover' → plural 'Britain-lovers') is a straightforward modern compound formation in English.

Individually, 'Britain' originally referred to the island(s) and territory called 'Britannia', and 'lover' has long meant 'one who loves'. Combined, the compound has the straightforward current meaning 'people who love Britain' without any major semantic shift from the component words.