Lewis Short
(verb) : ăcerbo, āvi, ātum, 1, id. (vox Vergil.).
* To make harsh or bitter, to embitter; lit. and trop. (very rare): gaudia,Stat. Th. 12, 75: mortem,Val. Fl. 6, 655.— Hence in an extended sense
* To augment or aggravate any thing disagreeable (cf. acuo): formidine crimen acerbat,Verg. A. 11, 407: nefas Eteoclis,Stat. Th. 3, 214.
Charlton T. Lewis, Charles Short, A Latin Dictionary