Intravenous can be broken down to intra-, meaning "within" or "via," and venous, meaning "of the veins." Often in hospitals you will be given water or nutrients from intravenous drips — you've surely seen these on TV if not at the hospital: plastic bags of liquid connected to a tube going into someone's arm. It's a way to get needed stuff into your body without waiting for the digestive system to handle it.