Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
per-tĕrĕbro, āvi, ātum, 1, v. a., to bore through: columnam, Cic. Div. 1, 24, 48: lapis perterebratus, Vitr. 8, 7, 8; Arn. 3, 107.