Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
obrepto, āvi, 1, v. freq. n. [id.], to steal on unawares, to come on imperceptibly (very rare): ne quis obreptaverit, Plaut. Pers. 1, 2, 27: obreptantibus Satyris, Plin. 35, 10, 36, § 109 (but in Cic. Att. 6, 5, 3, the correct read. is obrepebat).