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/ɹəˈtɜɹnləs/ · adjective
from (or due to) which one will not, or cannot, return (of a journey, destination, situation, distance, etc.).
Seventeen years had rolled on their returnless flight since that night of withering sorrow.
They would do an immensity of labor on their returnless journey to the ocean.
You must hear the judge's decision, remorselessly giving up the woman with her children born and unborn, into the hands of their claimants--by them to be carried to the slave prison, and thence to be sold to a returnless distance from the remaining but scattered fragments of her once happy family.
—but now false Memory loosed Her time-worn cable from the wilder'd mind, Blotting the chart whereon it loved to gaze Mid the dim ocean of returnless years.—
Pass on, returnless year!
Use returnless when its meaning, tone and grammar fit the full sentence. A synonym is not always a direct replacement.
Returnless means from (or due to) which one will not, or cannot, return (of a journey, destination, situation, distance, etc.).
The closest synonym depends on the sentence and intended sense.
The opposite depends on the specific sense.
Seventeen years had rolled on their returnless flight since that night of withering sorrow.
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