means Stern is the rear part of a ship or boat — though as an adjective it also means strict, severe, or unsmilingly firm.

from The boat-related 'stern' comes from Old Norse 'stjórn,' meaning steering or control — fittingly, since the rear of a vessel is where the rudder and the steering happen. The unrelated adjective 'stern' (severe, harsh) descends from Old English 'styrne,' a Germanic word probably tied to a root meaning 'rigid' or 'stiff.' Two different sterns, one steering ships and the other steering misbehaving children, fused into a single spelling by coincidence.