noun-modifying (irregular)
impossible; unfulfillable; unrequited; hopeless
Used prenominally to describe dreams, wishes, or love that cannot come true. Often carries a poetic or resigned tone.
それは叶わぬ夢だと分かっていた。
I knew it was an impossible dream.
叶わぬ恋に悩む日々が続いた。
Days of suffering from unrequited love continued.
Classical negative form of 叶う (to come true). The ぬ ending is an archaic negative auxiliary equivalent to modern ない, preserved in literary and poetic contexts.