Lewis & Short

†† gaesum, less correctly gēsum, i, n. [Celtic], a long, heavy javelin of the Gauls; Gr. γαισός or γαῖσον (syn.: dolo, sarissa, sparus, lancea), Caes. B. G. 3, 4, 1; Liv. 8, 8, 5; 9, 36, 6; 26, 6, 5; Varr. ap. Non. 555, 13; Verg. A. 8, 662; Sen. Hipp. 111; cf.: gaesum grave jaculum, Paul. ex Fest. p. 99 Müll. N. cr.
In poets the weapon of the Africans, Sil. 2, 444; of the Greeks, Stat. Th. 4, 64.

gēsum, i, v. gaesum.