unfulfilled dream; impossible dream
A literary or poetic expression for a dream that remains unseen to the end, often implying an unattainable or forever unfinished aspiration. The form 見果てぬ is a classical negative of 見果てる (to see through to the end).
See also: 見果てる
He kept chasing an unfulfilled dream.
That plan ended up as an impossible dream.
From 見果てる (to see through to the end) in its classical negative form 見果てぬ (not having seen through) + 夢 (dream). The phrase is a set expression meaning a dream that cannot be fully realized.