Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
perfŏrācŭlum, i, n. [perforo], a borer, an auger or gimlet (post-class.), Arn. 6, 200; cf. perforaculum, τρύπανον, τέρετρον, Gloss. Philox.