Definition of longtime. : having been so for a long time : long-standing a longtime friend a longtime friendship.Click to see full answer. Regarding this, what do you call a long time friend?Noun. Friend for an extended period. long-term friend. longtime friend.Also Know, which is correct longtime or long time? long time = noun phrase: I haven’t see you in a long time. longtime = adjective: They are longtime friends. Just so, what is a lifelong friend? A lifelong friend is that one friend who you knew as a child and who is still your friend through adulthood. This is the friend who has seen you through great times and bad times. The one with whom when things get really bad you can pick up the phone and call and she or he is on the other end with no judgments.What makes a long lasting friendship?Like any relationship, it starts by having common interests, caring about one another, and spending time together. Over time, you nurture that relationship, making sure to take time for each other even when you’re both busy.