'intracranial' originates from Latin, specifically the prefix 'intra-' meaning 'within' and the noun 'cranium' meaning 'skull' (the latter ultimately from Greek 'kranion').

'intracranial' was formed in modern English by combining Latin 'intra-' with the adjective 'cranial' (from Latin 'cranium', from Greek 'kranion'), producing the sense 'within the skull'.

Initially it meant 'within the skull', and over time it has retained this specific anatomical/medical meaning.