Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
serrācŭlum, i, n., a steering-oar, rudder: πηδάλιον, clavus navis, Gloss. Philox.; Dig. 9, 2, 29, § 2 dub. (others, servaculum or feraculum).