Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
impŏs (inp-), ŏtis, adj. [2. in-potis; cf. the opp., compos], not master of, not possessed of, without power over (ante- and postclass.): homo, animi impos, Plaut. Trin. 1, 2, 94: sui est impos animi, id. Cas. 3, 5, 7; id. Bacch. 4, 3, 3: mentis, Suet. Aug. 19 fin.; Lact. de Ira Dei, 21, 3: sui, Sen. Ep. 83, 3; Sen. Agm. 178; and absol., App. Dogm. Plat. 2, p. 22; cf.: impos est, qui animi sui potens non est, qui animum suum in potestate non habet, Paul. ex Fest. p. 109 Müll.: impos sui amore caeco, Sen. Agm. 117: veritatis, not partaking of, without, App. de Deo Socr. init. p. 43: damni, unable to bear, Aus. Idyll. 10, 274.