Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ē-languesco, gui, 3, v. inch. n., to grow faint, feeble, to slacken, relax (not ante-Aug.): ut elanguescendum aliena ignavia esset, Liv. 1, 46, 7; so in the praes., id. 35, 45; Vell. 2, 111 fin.; Plin. 9, 30, 48, § 91; Sil. 4, 140 al.
In the perf.: elanguimus, patres conscripti, nec jam ille senatus sumus qui, etc., Tac. H. 4, 42 fin.; Suet. Galb. 1: differendo deinde elanguit res, Liv. 5, 26, 3; cf.: neque tamen elanguit cura hominum eā morā, id. 23, 23, 8; so Gell. 16, 3, 2; Val. Fl. 4, 572.