Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sŭb-ŏrĭor, īri, v. dep. n., to spring up, arise, proceed (very rare), Lucr. 1, 1036; 1, 1049; 2, 1138: metallorum opulentia tot saeculis suboriens, Plin. 2, 93, 95, § 207; Arn. 3, 9.