Companion: Someone that you spend a lot of time with or someone who you travel with. Acquaintance: Someone that you know and have met, but you do not know a lot about them. A companion can be a friend, a partner or someone you travel with, you spend a lot of time with this person and you might know them very well. An acquaintance is just someone you know of, you know their name and maybe where they work, but you do not spend a lot of time with them or tell them things you might tell your close friends. An acquaintance could be your friend's colleague or someone you met at a function.