(of a person or their manner) serious and unrelenting, especially in asserting authority or exercising discipline

a smile transformed his stern face

Mama looked stern

(of competition or opposition) putting someone or something under extreme pressure

the past year has been a stern test of the ability of British industry

the rearmost part of a ship or boat

he stood at the stern of the yacht

A star.

In various other uses of "star".

A small amount of something; a grain, particle; a pinch; a portion. Compare starnie.