From best friend to deadliest enemy, and all the variations between. Here are some common words and phrases to describe friendship in English.

BFF (best friends forever)

best mate = your best friend.

a good friend = someone in your "inner circle" of friends.

to be really close to someone = be good friends with

pal = friend (UK slang)

buddy (best buddy) = friend (mainly US English)

to go back years = to know someone for a long time: "Steve and I go back years."

an old friend = a friend you've known for a long time: "He's an old friend of Dave's."

a friend of the family / a family friend = someone close to your family: "John was an old family friend."

a trusted friend = someone you can trust

a childhood friend = a friend from when you were very young

a circle of friends = all the friends in your group: "She's got a great circle of friends."

be just good friends = when you want to say you're only friends with someone of the opposite sex: "We're not going out. We're just good friends, that's all."

More casual friendships

penpal / epal = someone you know from corresponding / writing: "Find a penpal on our Penpals forum!"

someone you know from work (or another interest group): "Andy? Oh, he's someone I know from work."

someone you know to pass the time of day with = someone you know to say "hello" to.

casual acquaintance = someone you don't know very well: "She's just a casual acquaintance of mine."

a friend of a friend = someone you only know because they're a friend of one of your friends. "Dave's a friend of a friend."

a mutual friend = someone that two people know: "Karen's a mutual friend of both me and Rachel."

Mates

classmate = someone in your class at school.

workmate = someone you work with

flatmate (UK English) roommate (US English) = someone you share a flat or house with

soul mate = someone you're very close to because you share the same opinions and beliefs

Not good friends

on-off relationship = where you're sometimes friendly, and sometimes not: "Cath and Liz have an on-off relationship."

fair-weather friend = a friend who's never around when you need help: "She's only a fair-weather friend."

a frenemy = someone who's a friend and an enemy at the same time.

Other expressions

strike up a friendship with = make friends with someone

be no friend of = not like someone / something: "I'm no friend of his!"

have friends in high places = know important / influential people: "Be careful what you say. He's got friends in high places."