This is the 13642nd most frequent Russian word.
неисполненной
"Unfulfilled" or "not carried out."
The word 'неисполненной' here is used to describe 'мечте' (dream), indicating that the dream has not been fulfilled or realized.
Причина конфликта лежала в неисполненной мечте.
The reason for the conflict lay in an unfulfilled dream.
In this sentence, 'неисполненной' qualifies 'задача' (task), highlighting that the task hasn't been completed or carried out.
Задача осталась неисполненной, несмотря на все усилия.
The task remained unfulfilled despite all efforts.
The word 'неисполненной' modifies 'просьбе' (request), signifying that the request was not granted or answered.