The Collaborative International Dictionary of English v.0.48:
Hardy \Har"dy\ (h[aum]r"d[y^]), a. [Compar. Hardier
(-d[i^]*[~e]r); superl. Hardiest.] [F. hardi, p. p. fr. OF.
hardir to make bold; of German origin, cf. OHG. hertan to
harden, G. h[aum]rten. See Hard, a.]
1. Bold; brave; stout; daring; resolute; intrepid.
Hap helpeth hardy man alway. --Chaucer.
2. Confident; full of assurance; in a bad sense, morally
3. Strong; firm; compact.
[A] blast may shake in pieces his hardy fabric.
4. Inured to fatigue or hardships; strong; capable of
endurance; as, a hardy veteran; a hardy mariner.
5. Able to withstand the cold of winter.
Note: Plants which are hardy in Virginia may perish in New
England. Half-hardy plants are those which are able to
withstand mild winters or moderate frosts.