'intravenous' originates from Latin, specifically the elements 'intra' and 'vena', where 'intra-' meant 'within' and 'vena' meant 'vein'.

'intravenous' entered medical English via New Latin/Modern Latin 'intravenosus' (or similar formations) and evolved into the Modern English adjective 'intravenous'; the adverb 'intravenously' formed by adding the adverbial suffix '-ly'.

Initially it meant 'within or into a vein', and over time it has retained this medical sense, now commonly used to describe administration directly into the bloodstream.