'pro-British' originates from Latin and Old English elements: the prefix 'pro-' (from Latin 'pro') and 'British' (from Old English 'Bryttisc', ultimately from Latin 'Britannia'), where 'pro-' meant 'for, in favor of' and 'Bryttisc' meant 'of the Britons'.

'pro-' (Latin 'pro') combined with Middle English and Modern English uses of 'British' (from Old English 'Bryttisc' and Latin 'Britannia') to form compound expressions meaning 'for Britain' or 'supporting Britain'; over time compounds using 'pro-' + nationality (e.g. 'pro-American', 'pro-French') became common, leading to modern usage 'pro-British'.

Initially the elements signified literally 'for the Britons' or 'in favor of Britain'; over time the compound has been used broadly to mean supportive of Britain, its government, policies, institutions, or culture.