Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
complēmentum, i, n. [compleo], that which fills up or completes, a complement (rare; only fig.): numerorum (inania quaedam verba), * Cic. Or. 69, 230: omnium accusationum, that gives them their full weight, Tac. A. 3, 38: accusationis, Cod. Th. 9, 24, 3.