Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ob-tĕnebro, āre, v. a., to make dark, to darken (eccl. Lat.): obtenebrabitur dies lucis (al. tenebrabitur), Lact. 4, 19: stellae, Vulg. Job, 3, 9: lux, id. Isa. 5, 30: sol, id. ib. 13, 10: dies, id. Mic. 3, 6.