The answer to the crossword for the term THE 'I' IN IV is INTRA. Intra is a Latin prefix meaning 'WITHIN' or 'INSIDE'. It is commonly used in medical terminology to refer to something that occurs WITHIN the body, such as an intra-abdominal infection. In the context of the phrase 'the 'I' in IV', it refers to the intravenous administration of fluids or medications, which is done by inserting a needle into a vein and delivering the substance directly into the bloodstream.