Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ŏb-īrascor, īrātus, 3, v. dep. n., to be angry at any thing (mostly post-Aug.; but cf. obiratio): obirascens fortunae animus, Sen. Tranq. An. 2, 11: cum male audiunt, obirascuntur. App. Mag. p. 275, 18; id. Flor. 3, p. 357.
Hence, ŏbīrātus, a, um, P. a., angered, angry: fortunae obirati, Liv. 1, 31; 42, 10; Sen. Ep. 56, 9; id. Const. 19, 2.