hard

\ \ [OE] Hard comes ultimately from a prehistoric Indo-European *krátus, which denoted ‘power, strength’. This original meaning was carried over into Greek krátos ‘strength, power, authority’ (source of the ending -cracy in such English words as democracy and plutocracy), but the Germanic languages took it over mainly in the sense ‘resistant to physical pressure’. The prehistoric Germanic form *kharthuz produced, besides English hard, German hart, Dutch hard, Swedish hård, and Danish haard. The sense ‘difficult’, incidentally, developed in the 14th and 15th century from the notion ‘resistant to one’s efforts’.

\ \ A Germanic derived verb *kharthjan ‘harden’ was borrowed into Old French as hardir ‘embolden’, and its past participle hardi ‘bold’ reached English as hardy [13]. Its main modern sense, ‘robust, tough’, presumably a harking back to its distant English relative hard, developed in the 16th century.

\ \ Cf.⇒ HARDY