Long-time means having held the same role or friendship for very many years. A long-time colleague.
It goes before the noun, where long time as two words does not. A long-time supporter is trusted differently from a recent one, fairly or not.
1adjectivelong-timeHaving held the same role or friendship for very many years.
“His long-time partner ran the business side entirely.”
long-time is a quality.
longtime comes from long + time.
Etymology from Wiktionary, CC BY-SA