I think this is the poem, ' Give hope to the race of man. I cannot keep hope in myself:'
Ónen i-Estel Edain, ú-chebin estel anim.
The only known example of a linnod, a certain type of Sindarin poetry.
Indeed, Narya! Quoting the Lord of the Rings:
"But she answered only with this linnod: ónen i-Estel Edain, ú-chebin estel anim, and Aragorn went away heavy of heart. Gilraen died before the next spring.
Tolkien provided a translation "I gave Hope to the Dunedain, I have kept no hope for myself", but he modified it later as he developed his ideas on negation. Parma Eldalamberon 22 shed some light on this development:
úchebin in Gilraen's linnod will not fit so well. It must be assumed that in S. ú was used as a verbal as well as an adjectival prefix, with a meaning intensified to 'impossible' so that it came near to a negative. The nuance will remain important. úchebin will mean not 'I do not keep', but 'I cannot keep'.