This is the 169th most frequent Hungarian word.
egyetlen
"Only" or "single."
Here, 'egyetlen' emphasizes the exclusivity of the solution being the sole one.
Egyetlen megoldás létezik erre a problémára.
There is only one solution to this problem.
In this example, 'egyetlen' stresses the complete absence of truthful words.
Nem mondott egyetlen igaz szót sem.
He did not say even a single truthful word.
'Egyetlen' highlights the uniqueness of the friendship here.