prosthesis

Via Latin, from Ancient Greek πρόσθεσις (prósthesis, “addition”), from προστίθημι (prostíthēmi, “to add”), from πρός (prós, “towards”) + τίθημι (títhēmi, “to place”), from Proto-Indo-European *próti, *préti + *dʰédʰeh₁ti (“to be putting, to be placing”). By surface analysis, prosth- +‎ -esis.