c. 1200, "bold, daring, fearless," also "presumptuous, audacious," from Old French hardi "bold, brave, courageous; confident, presumptuous," from past participle of hardir "to harden, be or make bold," from Frankish *hardjan "to make hard" (source also of Old Frisian herda, Old High German herten, Old Norse herða, Gothic gahardjan "make hard"), from Proto-Germanic *hardu- (from PIE root *kar- "hard"). Sense influenced by English hard. Of plants, "able to survive in the open year-round," 1660s. Related: Hardily; hardiness. Hardhede "physical hardiness" is attested from early 15c.