Do you have more context or a complete sentence?
"ehrnen" could be the shortened Form of the declined adjective "ehern" like in "Er trug einen eh(e)rnen Ring." (He wore an iron ring.)
In this context the outdated word "ehrnen" would mean "out of iron".
However, I have no idea what this word could mean if it's no adjective but a verb.
Thanks Trance and Lykurg
My fault entirely; the word is from a poem by Goethe in his poems in Ilmenau (1783) and it says: " Naxh ewigen, ehrnen, Grossen Gesetzen Müssen wirt alle Unseres Daseins Kreise vollenden"
It makes sense to translate it as "effort" but, althoug I speak and read german, I am not german and have doubts. Thanks for the help!