bi ‧ on ‧ ic /baɪˈɒnɪk $ -ˈɑːn-/ BrE AmE adjective
[ Date: 1900-2000 ; Origin: bionic 'using electronically controlled parts in the human body' (20-21 centuries) , from bio- + electronic ]
bionic arms, legs etc are electronic and therefore stronger or faster than normal arms etc – often used humorously:
I swear Mom has bionic ears.