Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. instrātus, a, um, Part., from insterno.
* 2. in-strātus, a, um, adj. [2. insterno], not covered or spread over: cubile, an unspread couch, Verg. G. 3, 230 (so interpp. plur. ad loc.; but it is better to construe instrato as part. of insterno, with frondibus hirsutis; cf.: instrata cubilia fronde, Lucr. 5, 987 Wakef. ad loc.).