Sea change refers to a big and sudden change or transformation.

// The early 2000s witnessed a sea change in public opinion about smoking in public places.

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“Over the course of my grandmother’s lifetime, gender expectations for women underwent a sea change. My grandmother ended up pursuing an education and becoming a doctor, leading an independent life that made her mother proud.” — Wendy Chen, LitHub.com, 20 May 2024

In The Tempest, William Shakespeare’s final play, sea change refers to a change brought about by the sea: the sprite Ariel, who aims to make Ferdinand believe that his father the king has perished in a shipwreck, sings within earshot of the prince, “Full fathom five thy father lies...; / Nothing of him that doth fade / But doth suffer a sea-change / into something rich and strange.” This is the original, now-archaic meaning of sea change. Today the term is used for a distinctive change or transformation. Long after sea change gained this figurative meaning, however, writers continued to allude to Shakespeare’s literal one; Charles Dickens, Henry David Thoreau, and P.G. Wodehouse all used the term as an object of the verb suffer, but now a sea change is just as likely to be undergone or experienced.