Friend, acquaintance, intimate, confidant are comparable when they designate a person, especially not related by blood, with whom one is on good and, usually, familiar terms.
Friend, in its application, ranges from a person who is not hostile or is a well-wisher to a person whose society one seeks or accepts with pleasure because of liking, respect, or affection.
Acquaintance is applied to a person with whom one is on speaking terms. However, when these words are used in contrast, both imply a degree of familiarity, friend distinctively connoting close bonds of love and affection and acquaintance, comparative infrequency of contact and less close personal interest.
This distinction is not invariably observed, especially when acquaintance is used as a collective plural.
Intimate adds to friend the implications of a depth of affection and a closeness of association that tend to preclude reserve.
Confidant usually designates that intimate who actually is entrusted with one’s secrets or is admitted to confidential discussions.