Lewis & Short

ūmesco (less correctly hū-), no perf. nor sup., ĕre, 3, v. inch. n. [umeo], to grow moist or wet (poet. and in post-Aug. prose): (equi) umescunt spumis, Verg. G. 3, 111: cortex non umescit, Plin. 17, 14, 24, § 107: terra umescens rore occulto, id. 18, 34, 77, § 339: solum, Pall. Sept. 10, 3: vidimus umescentes oculos tuos, Plin. Pan. 73, 4.