I was writing my history essay earlier today on the effects of the First World War and in my conclusion I was comparing the four causes I had discussed in the essay.
I then was half-way through my sentence when I struggled to think of the superlative of long-term.
the longest-term cause was...
the most long-term cause was...
struck me as viable options, however neither sounded correct to me at the time. I also thought of
most chronic afterwards, although by then it was too late. Greatest also perhaps connotes importance, which is undesirable in the context.
In the end I rephrased my sentence to escape the predicament and although I cannot remember what I wrote instead I believe it was less effective than a sentence with the superlative of long-term.