Attenuate ultimately comes from a combining of the Latin prefix ad-, meaning "to" or "toward," and tenuis, meaning "thin," a pedigree that is in keeping with the English word's current meanings, which all have to do with literal or metaphorical thinning. The word is most common in technical contexts, where it often implies the reduction or weakening of something by physical or chemical means. You can attenuate wire by drawing it through successively smaller holes, for example, or attenuate gold by hammering it into thin sheets. Current evidence dates the term to the 16th century, in which we find many references to bodily humors in need of being attenuated; modern medicine prefers to use the word in reference to procedures that weaken a pathogen or reduce the severity of a disease.