Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
in-strēnŭus, a, um, adj., not brisk, inactive, sluggish, spiritless (poet. and in post-Aug. prose): homo, Plaut. Most. 1, 2, 23: animus, Ter. Heaut. 1, 1, 68: dux, Suet. Vesp. 4.
Adv.: instrēnŭē, without spirit: non instrenue moriens, Just. 17, 2, 1.