stern (adj.)
Old English styrne "severe, strict, grave, hard, cruel," from Proto-Germanic *sternijaz (cognates: Middle High German sterre, German starr "stiff," störrig "obstinate;" Gothic andstaurran "to be stiff;" Old Norse stara; Old English starian "to look or gaze upon"), from PIE root *ster- (1) "rigid, stiff" (see stereo-). Related: Sternly; sternness.
stern (n.)
early 13c., "hind part of a ship; steering gear of a ship," probably from a Scandinavian source, such as Old Norse stjorn "a steering," related to or derived from styra "to guide" (see steer (v.)). Or the word may come from Old Frisian stiarne "rudder," which also is related to steer (v.). Stern-wheeler as a type of steam-boat is from 1855, American English.